Hesitation from idle to ~1500 RPM with modest+ throttle

[Assimilator1]

No I'm not in the habit of lugging it before anyone says that .

So this started a couple of years ago, initially only when the engine was stone cold (say upto 30s running) + cold temp's, pull away in 1st, roughly 1/4 to 1/2 throttle ~1500 RPM, it'd hesitate for about a second.
Because this scenario was rare and brief I just ignored it.
Fastforward to today and it has gradually got worse and worse, happening at increasing engine temp and ambient temps, and at less throttle (but always up to about 1500 RPM).
The other week the engine was a needles width from fully warmed up, when a work mate asked me to rev it up (of course I was willing to oblige! ), it spluttered (hesitated) then revved up (slightly embarrassing, lol). So it's getting to be quite a problem now.
Blipping the throttle from idle (to say 2k RPM) will replicate it, the colder the engine and ambient temps are, the worse it is. More throttle makes it worse too (obviously I don't give it full throttle when cold!).
It reminds me of 2 cars I had when I was young (Mk1 Fiesta's), these had carbs with a manual choke, if I pushed the choke in too soon, they would hesitate just like that! lol. So it seems like a weak mixture misfire on snapping open the throttle from low revs.

No EML has shown, there are no engine codes (pending or current), I tried to read live data from the o2 sensors, but apparently that's not possible with these (I used ISTA, an old version, and my work's snap on tool).
I did do a primary o2 sensors check with ISTA, and it found no problems, giving the sensors a very good score of 0.9.
I also did a spark duration check @idle, which was mostly in the range of 0.65-0.75 (which is in spec, spec 01.-1.5ms). And I checked combustion quality @ idle, which mostly was between 0.4 -1.3 (which is in range too, spec 0-5).

I use SUL fuel (99 octane), spark plugs have done 25k miles, IIRC the OE change interval is 36k miles? I was planning to change them at 30k.

If it is a weak mixture issue, then unmetered air could be getting in. I suppose I need to check air and vac hoses.

Standard s/w ([edit] tune/map) AFAIK, TAs were replaced just a couple of months before I bought the car! . Although that was 5 1/2 yrs ago now, they are rebuild.org TAs and the car's only done about 12k miles since then.
I also very recently lubed the throttle linkage pivots/bearings with dry PTFE.
Did the ITB test and got a 'not ok' on 1 of bank 2's test, but still no error codes. Not had the chance to find out what this results means.
[edit] 2008 car, 86k miles

Checked inlet man. pressure sensor plausibility, that's good.
Turns out these don't have a MAF, lol. [edit] Correction, turns out they do, but only for the secondary air system (air injection system).

I wondered if anyone else has had this, and what cured it for them?

[m3s65b4.x]

Originally Posted by Assimilator1

...
Fastforward to today and it has gradually got worse and worse, happening at increasing engine temp and ambient temps, and at less throttle (but always up to about 1500 RPM).
The other week the engine was a needles width from fully warmed up, when a work mate asked me to rev it up (of course I was willing to oblige! ), it spluttered (hesitated) then revved up (slightly embarrassing, lol). So it's getting to be quite a problem now.
Blipping the throttle from idle (to say 2k RPM) will replicate it, the colder the engine and ambient temps are, the worse it is. More throttle makes it worse too (obviously I don't give it full throttle when cold!).

No EML has shown, there are no engine codes (pending or current), I tried to read live data from the o2 sensors, but apparently that's not possible with these (I used ISTA, an old version, and my work's snap on tool).
I did do a primary o2 sensors check with ISTA, and it found no problems, giving the sensors a very good score of 0.9.
I also did a spark duration check @idle, which was mostly in the range of 0.65-0.75 (which is in spec, spec 01.-1.5ms). And I checked combustion quality @ idle, which mostly was between 0.4 -1.3 (which is in range too, spec 0-5).
...

I wondered if anyone else has had this, and what cured it for them?

Expierenced same symptoms and that very odd. Replaced spark plugs, TA's (one got limp mod), fuel pressure sensor, final drive gear ratio to 4.44, later all new OEM ign.coils, 240E based software.
After that most hesitation like 95% is gone but with cold engine, colder weather, fast throttle you can expect that notorious hesitation. When fully warmed up there still 1-2% probability it will hesitate in some situation.
This is nuisance but can accept.

[Assimilator1]

Originally Posted by m3s65b4.x

Experienced same symptoms and that very odd. Replaced spark plugs, TA's (one got limp mod), fuel pressure sensor, final drive gear ratio to 4.44, later all new OEM ign.coils, 240E based software.
After that most hesitation like 95% is gone but with cold engine, colder weather, fast throttle you can expect that notorious hesitation. When fully warmed up there still 1-2% probability it will hesitate in some situation.
This is nuisance but can accept.

Interesting, any one thing (or set of things) make a particularly noticeable difference?

[Space Horse]

Originally Posted by Assimilator1

No I'm not in the habit of lugging it before anyone says that .

So this started a couple of years ago, initially only when the engine was stone cold (say upto 30s running) + cold temp's, pull away in 1st, roughly 1/4 to 1/2 throttle ~1500 RPM, it'd hesitate for about a second.
Because this scenario was rare and brief I just ignored it.
Fastforward to today and it has gradually got worse and worse, happening at increasing engine temp and ambient temps, and at less throttle (but always up to about 1500 RPM).
The other week the engine was a needles width from fully warmed up, when a work mate asked me to rev it up (of course I was willing to oblige! ), it spluttered (hesitated) then revved up (slightly embarrassing, lol). So it's getting to be quite a problem now.
Blipping the throttle from idle (to say 2k RPM) will replicate it, the colder the engine and ambient temps are, the worse it is. More throttle makes it worse too (obviously I don't give it full throttle when cold!).
It reminds me of 2 cars I had when I was young (Mk1 Fiesta's), these had carbs with a manual choke, if I pushed the choke in too soon, they would hesitate just like that! lol. So it seems like a weak mixture misfire on snapping open the throttle from low revs.

No EML has shown, there are no engine codes (pending or current), I tried to read live data from the o2 sensors, but apparently that's not possible with these (I used ISTA, an old version, and my work's snap on tool).
I did do a primary o2 sensors check with ISTA, and it found no problems, giving the sensors a very good score of 0.9.
I also did a spark duration check @idle, which was mostly in the range of 0.65-0.75 (which is in spec, spec 01.-1.5ms). And I checked combustion quality @ idle, which mostly was between 0.4 -1.3 (which is in range too, spec 0-5).

I use SUL fuel (99 octane), spark plugs have done 25k miles, IIRC the OE change interval is 36k miles? I was planning to change them at 30k.

If it is a weak mixture issue, then unmetered air could be getting in. I suppose I need to check air and vac hoses.

Standard s/w AFAIK, TAs were replaced just a couple of months before I bought the car! . Although that was 5 1/2 yrs ago now, they are rebuild.org TAs and the car's only done about 12k miles since then.
I also very recently lubed the throttle linkage pivots/bearings with dry PTFE.
Did the ITB test and got a 'not ok' on 1 of bank 2's test, but still no error codes. Not had the chance to find out what this results means.

Checked inlet man. pressure sensor plausibility, that's good.
Turns out these don't have a MAF, lol.

I wondered if anyone else has had this, and what cured it for them?

Well, I am going to say some stupid things to try and help lol. But with My car with a SC and being living at 6000+ feet I can definitely say fuel/air ratios are important.

My immediate response would be the TAs, but with them "fixed" I don't think it is them.

When my engine is cold (below freezing is worse), the engine almost refuses to rev. I think the mechanical limitations from the blower and it being cold where I think the ECU might step in to stop fuel flow, you have to convince the car to rev with several presses of the throttle. This is all happening in neutral.

However, once the car is warm, I have no issue and it's happy to scream. My car is also way happier and easier to drive (6MT) at Power or Power+ throttle mode.

Before anything else, I would try driving the car in power and/or power+. I know it makes a world of difference on my car for what the peddle does. I really think BMW did some weird things with the throttle peddle when in normal mode. There feels like a lot of dead space where nothing happens. Very poor modulation in what the throttle does in terms of 0-15 vs. 20-30 vs 60-80 (MPH)

This is tune dependent but if I am launching my car and I go from 100% throttle 1st gear, and I accidentally (I have done this a lot) let off the throttle to 80% at around 6500 RPM the car will almost stop increasing in revs and even once I go back to 100% the car will still behave the same.

I would seriously try the car with power and/or power+ even when cold. It might at least help narrow down the issue. As we all are familiar tune re-flashing, your throttle might simply need to be tuned.

My examples which are just like yours, either go away or are in angry driving. So, for it to still occur even when the car has been fully warmed up is odd.

Another thing I have run into, when I haven't driven my car for a weeks or months. There is quite a lot of condensation build up within the exhaust and the car will spray out a load of water and struggle to start and then continue to spray for the next 30mins. I think it is impossible for a hot exhaust to have any water that isn't a very hot vapor, but we are talking about an unknown.

I think it is on the fuel side, even though a failed ITB test might point to an air issue. Maybe it is a fuel pump issue.

I'm gonna say something stupid. Are you ready? Are you sure?

Your octane is too high? Hear me out.

My VF-595 supercharged s65 runs on 91 octane even at sea-level. We are talking about weird, freaky, gremlins that are not leaving. I would think anything is possible. I am not familiar with what modifications you have but if it is mostly stock, maybe try a tank of 93 octane if you are comfortable with it.

All I am going to say is octane can be too high. Not familiar with where this engine is at in particular. If others have had no problem running SUL 99, then please ignore me for my absolutely outrageous reasoning.

[m3s65b4.x]

Originally Posted by Assimilator1

Interesting, any one thing (or set of things) make a particularly noticeable difference?

Main culprit were degraded coils in my case but for performance most noticeable difference make stg2 tune with freeflow exchaust and FD change.
Fresh plugs are maintenace items, TA's are mandatory, after sensor replace car clearly pulled harder.

Please let us know which results you'll achieve and particularly cured and get rid off that low rpm hesitation.

[DrFerry]

My two cents about a possible root cause:

1. Fuel quality makes a difference
2. Carbon deposits in/on the injectors and plugs
3. Fuel pressure sensor
4. Manifold pressure sensor
5. Differential pressure sensor
6. Carbon deposits in the ICV

.

[Assimilator1]

Space Horse Just a quick reply for now (I'll reply fully later), but I am in the UK and we use different octane rating to the US. e.g regular UL is 95 Octane.

[Assimilator1]

Space Horse
Another thing I have run into, when I haven't driven my car for a weeks or months. There is quite a lot of condensation build up within the exhaust and the car will spray out a load of water and struggle to start and then continue to spray for the next 30mins. I think it is impossible for a hot exhaust to have any water that isn't a very hot vapor, but we are talking about an unknown.

I think it is on the fuel side, even though a failed ITB test might point to an air issue. Maybe it is a fuel pump issue.

A lot of water in the exhaust is usually a common issue with cars that do a lot of short journeys where it hasn't warmed up enough (assuming no head gasket or EGR cooler problems!). Most of the water comes from burning fuel, although I guess if you're in a high humidity climate that's going to add to it.
Anyway, in my years as a mechanic I've not come across this water build up in the exhaust causing any running or starting problems. Any water that is obstructing the exhaust would be blown out in seconds as the engine is fired up.
My M3 doesn't normally do short journeys anyway, the trip to the workshop is about the only one, which ordinarily would be once a month at most (for levels and pressures, but I normally do them at home now).

I wondered about a fuel pump too, but discounted it for 2 reasons, no fault codes and under full throttle (once past the hesitation) from (say) 2000-8300 RPM their is no problem with power delivery.
Also, on Bedford Autodrome circuit in May, along the longest straight I accelerated to ~142mph , redline in 4th gear, obviously WOT, their were no performance issues there either. This will be far more demanding on the pump than a brief snapping open of the throttle at ~1500 RPM.

Further to my octane comment earlier, according to Wiki, apparently the US (Canada, Brazil and Mexico) uses AKI/PON rating for petrol, where as the UK and most of the rest of the world uses RON.
Petrol equivalents.
Standard (regular UL): 95 RON (equivalent to 91 AKI).
Premium _____ (SUL): 98 RON (equivalent to 93 AKI).
SUL 99 RON = 93-94 AKI (confusingly! So maybe 93.5 AKI? lol).

I would suggest your SC M3 could benefit from using 93 AKI octane petrol .

Re power/power+ setting, curious, you'd think the quick acting throttle would make the hesitation worse.
I could try that for diagnostic purposes, but not a permanent thing, as something is clearly getting worse.

Originally Posted by DrFerry

My two cents about a possible root cause:

1. Fuel quality makes a difference
2. Carbon deposits in/on the injectors and plugs
3. Fuel pressure sensor
4. Manifold pressure sensor
5. Differential pressure sensor
6. Carbon deposits in the ICV

.

Hmm, well point 1, I usually fill up using Tesco's (supermarket) SUL 99 RON petrol, depending what sources you read, it's either a 'meets bare min standards', or is 'just as good as premium fuels'. So who knows!?
But the problem has only been noticeable past 2-3 years and only more significant over the past year or so.
I've been using mostly Tesco fuel since I bought the car end of 2019.

Re point 2.
Injectors, is this even likely with port injectors? I know it certainly can be with DI injectors, but I thought port injectors pretty much avoided that.
Plugs, guess I'd have to take them out and have a look, but seeing as I do very few short journeys and do a couple of track days each year, I would've thought any carbon would get burnt off?

Point 3
Would need to test that, I'm pretty sure we have a fuel pressure gauge at work, but hooking it up is probably going to be easier said than done.
But this would also have the benefit of eliminating the pump.

For my future reference, from ISTA :-
13 31 Fuel Pump with Drive and Pipe S65
Fuel pressure when starting 5.55 - 6.85 bar
At idle approx. 800 rpm (engine at normal operating temperature) 3 bar

Point 4
Already tested, well at least as much as ISTA asks, which is basically to compare the IM press sensor reading to the ambient pressure reading with the engine off, they match, so seems good.

Point 5
What's that? lol

Point 6
(Idle control valve, right?).
Well that's interesting, I recently posted the following at m3cutters, but forgot to here.
"I did find a couple of weeks ago that I had forgotten to plug in the air intake feed pipe for the ICV from some months back! That said, when I plugged it back in it made no difference to the problem (and as far as I can see, the only issue that would cause is to have unfiltered air going into the ICV/engine )."
Perhaps some dirt has got in and is causing the ICV to stick open briefly? Although, that said, their is no problem with idle control.

On a separate issue, I earlier said that these don't have a MAF, but it actually turns out they do, not for the main inlet system, but the secondary air system. So something else I need to check!

[edit]
On further reflection, something I mentioned at m3cutters previously, I think I'm going to take the plenum off and check for air/vacuum leaks before going through the above items.

[DrFerry]

Originally Posted by Assimilator1

Point 5
What's that? lol

IF you've ever accidentally spilled brake fluid on the master cylinder the fluid can and often does drip onto the pressure sensor that's directly underneath the brake servo. Here's some links to the DIY thread etc.
.
https://www.m3post.com/forums/showthread.php?t=1338052
.
https://www.fcpeuro.com/products/bmw...or-34302283605
.

[DrFerry]

Originally Posted by Assimilator1

Hmm, well point 1, I usually fill up using Tesco's (supermarket) SUL 99 RON petrol, depending what sources you read, it's either a 'meets bare min standards', or is 'just as good as premium fuels'. So who knows!? But the problem has only been noticeable past 2-3 years and only more significant over the past year or so. I've been using mostly Tesco fuel since I bought the car end of 2019.

Octane is certainly one of the major factors that can affect engine hesitation, but carbon deposits are another. Hence, the fuel detergent additive package also becomes important as the engine and fuel system (injectors, valve seats etc) mileage increases. In the USA, a third party (AAA) which is similar to the U.K.'s A.A. did a fuel quality study. I've attached the .pdf report below and IMO it's well worth a read. Forum members are reporting S65 injector failures with resulting engine failures due to bore scoring or bent rods from hydro-locking - when fuel leaks into the combustion chamber. I merely mention this in case the hesitation you're experiencing is an early warning sign of injector failure due to carbon deposits or other types of fuel deposits (gummy varnish?) affecting the injector spray pattern. I recall certain YouTubers ferreting out which fuels were used in the AAA report - with the best one for detergent additives being Shell V-Power. It's part of the reason BMW recommends Top Tier fuels in the USA as well as Techron fuel system cleaner. But Forum users report Techron coats the S65 plugs. See attached AAA report.
.
https://www.m3post.com/forums/showthread.php?t=1898330
.

[Space Horse]

Originally Posted by Assimilator1

Space Horse
Another thing I have run into, when I haven't driven my car for a weeks or months. There is quite a lot of condensation build up within the exhaust and the car will spray out a load of water and struggle to start and then continue to spray for the next 30mins. I think it is impossible for a hot exhaust to have any water that isn't a very hot vapor, but we are talking about an unknown.

I think it is on the fuel side, even though a failed ITB test might point to an air issue. Maybe it is a fuel pump issue.

A lot of water in the exhaust is usually a common issue with cars that do a lot of short journeys where it hasn't warmed up enough (assuming no head gasket or EGR cooler problems!). Most of the water comes from burning fuel, although I guess if you're in a high humidity climate that's going to add to it.
Anyway, in my years as a mechanic I've not come across this water build up in the exhaust causing any running or starting problems. Any water that is obstructing the exhaust would be blown out in seconds as the engine is fired up.
My M3 doesn't normally do short journeys anyway, the trip to the workshop is about the only one, which ordinarily would be once a month at most (for levels and pressures, but I normally do them at home now).

I wondered about a fuel pump too, but discounted it for 2 reasons, no fault codes and under full throttle (once past the hesitation) from (say) 2000-8300 RPM their is no problem with power delivery.
Also, on Bedford Autodrome circuit in May, along the longest straight I accelerated to ~142mph , redline in 4th gear, obviously WOT, their were no performance issues there either. This will be far more demanding on the pump than a brief snapping open of the throttle at ~1500 RPM.

Further to my octane comment earlier, according to Wiki, apparently the US (Canada, Brazil and Mexico) uses AKI/PON rating for petrol, where as the UK and most of the rest of the world uses RON.
Petrol equivalents.
Standard (regular UL): 95 RON (equivalent to 91 AKI).
Premium _____ (SUL): 98 RON (equivalent to 93 AKI).
SUL 99 RON = 93-94 AKI (confusingly! So maybe 93.5 AKI? lol).

I would suggest your SC M3 could benefit from using 93 AKI octane petrol .

Re power/power+ setting, curious, you'd think the quick acting throttle would make the hesitation worse.
I could try that for diagnostic purposes, but not a permanent thing, as something is clearly getting worse.



Hmm, well point 1, I usually fill up using Tesco's (supermarket) SUL 99 RON petrol, depending what sources you read, it's either a 'meets bare min standards', or is 'just as good as premium fuels'. So who knows!?
But the problem has only been noticeable past 2-3 years and only more significant over the past year or so.
I've been using mostly Tesco fuel since I bought the car end of 2019.

Re point 2.
Injectors, is this even likely with port injectors? I know it certainly can be with DI injectors, but I thought port injectors pretty much avoided that.
Plugs, guess I'd have to take them out and have a look, but seeing as I do very few short journeys and do a couple of track days each year, I would've thought any carbon would get burnt off?

Point 3
Would need to test that, I'm pretty sure we have a fuel pressure gauge at work, but hooking it up is probably going to be easier said than done.
But this would also have the benefit of eliminating the pump.

For my future reference, from ISTA :-
13 31 Fuel Pump with Drive and Pipe S65
Fuel pressure when starting 5.55 - 6.85 bar
At idle approx. 800 rpm (engine at normal operating temperature) 3 bar

Point 4
Already tested, well at least as much as ISTA asks, which is basically to compare the IM press sensor reading to the ambient pressure reading with the engine off, they match, so seems good.

Point 5
What's that? lol

Point 6
(Idle control valve, right?).
Well that's interesting, I recently posted the following at m3cutters, but forgot to here.
"I did find a couple of weeks ago that I had forgotten to plug in the air intake feed pipe for the ICV from some months back! That said, when I plugged it back in it made no difference to the problem (and as far as I can see, the only issue that would cause is to have unfiltered air going into the ICV/engine )."
Perhaps some dirt has got in and is causing the ICV to stick open briefly? Although, that said, their is no problem with idle control.

On a separate issue, I earlier said that these don't have a MAF, but it actually turns out they do, not for the main inlet system, but the secondary air system. So something else I need to check!

[edit]
On further reflection, something I mentioned at m3cutters previously, I think I'm going to take the plenum off and check for air/vacuum leaks before going through the above items.

Unfortunately for me in the US, the octane supplied in gas stations varies at what altitude they are. Since Octane in fuel is usually only for compression, and when you are at higher altitude you don't need the same octane to reach the desired compression due to the air being thinner. So, the entire State of Colorado has 85-AKI, 87-AKI, and 91-AKI. It is incredibly hard to find anything higher than 91-AKI in my state or really any State that is higher than 4500 feet. Once you are in a lower altitude State then the pumps go to 87-AKI, 91-AKI, and 93-AKI.

There is also the argument that since the tune is at a certain octane and compression, that increasing octane won't necessarily do much. I don't exactly agree with that. I would definitely use higher octane if I could.

It is funny I have rented cars in the UK; I should know that your fuel is different.

What is the mileage of your car? That can definitely rule in/out whether carbon build up is a concern.

Also, what RPM are you usually at when cruising on the Highway? For how rich these cars run stock IMO (My SC tune makes it worse) unburnt fuel over long periods of not higher revs (3000+) will definitely start clogging things up.

These cars also have pretty aggressive camshafts. Have you checked the Camshaft or Crankshaft position sensors? My friend had an XJ Cherokee (Jeep) that had a camshaft sensor go bad which made it rev terribly. (Not here to say anything Jeep makes can even hold a candle to the mechanical marvel that the s65 is)

A camshaft in the wrong place in the wrong time frame can certainly affect what will happen when you stomp the gas. That could also explain it getting worse slowly over time. These already don't typically like low revs.

With how low the revs are when this is happening, might point to the cam being offset slightly when near idle. The engines probably mechanically fixing it and adjusting it to then freely rev (Redlining 4th is awesome .)

I know it isn't possible for it to be that far off. However, engines have cam position sensors for a reason.

[Scrippy]

I see all the typical ideas being brought up and I agree with them. I’ve had idle problems like hunting and stalling before and a new fuel vent valve fixed it. I’ve also had 1 of 2 TA’s fail (120,000ish miles) and prior to it failing I had idle issues like hunting, stalling and hesitation with gentle throttle application from a stop. Just this week my final OE TA failed (281,000) and I had idle hunting, stalling and hesitation with gentle throttle application from a stop. I finally got a code for bank 1 TA. I’ve opened both of the failed TA’s and the first 5-7 teeth are worn. This is the start range where the TA wakes on ignition and opens the throttles for start and idle. So I will bet you have 1 or both TA’s shitting the bed on ya. Good luck.

[tdott]

What tune are you on?

I've seen certain tunes that did not throw a check engine light, but as soon as stock 240E/241E was flashed back, there was a CEL and misfire code that led to a bad coil causing a slight hesitation/shudder at low rpm. Sounds like it might be similar to your issue.

[Assimilator1]

Originally Posted by DrFerry

IF you've ever accidentally spilled brake fluid on the master cylinder the fluid can and often does drip onto the pressure sensor that's directly underneath the brake servo. Here's some links to the DIY thread etc.
.
https://www.m3post.com/forums/showthread.php?t=1338052
.
https://www.fcpeuro.com/products/bmw...or-34302283605
.

Re vacuum pressure sensor, is that not just used for brake assistance/servo control?

Originally Posted by DrFerry

Octane is certainly one of the major factors that can affect engine hesitation, but carbon deposits are another. Hence, the fuel detergent additive package also becomes important as the engine and fuel system (injectors, valve seats etc) mileage increases. In the USA, a third party (AAA) which is similar to the U.K.'s A.A. did a fuel quality study. I've attached the .pdf report below and IMO it's well worth a read. Forum members are reporting S65 injector failures with resulting engine failures due to bore scoring or bent rods from hydro-locking - when fuel leaks into the combustion chamber. I merely mention this in case the hesitation you're experiencing is an early warning sign of injector failure due to carbon deposits or other types of fuel deposits (gummy varnish?) affecting the injector spray pattern. I recall certain YouTubers ferreting out which fuels were used in the AAA report - with the best one for detergent additives being Shell V-Power. It's part of the reason BMW recommends Top Tier fuels in the USA as well as Techron fuel system cleaner. But Forum users report Techron coats the S65 plugs. See attached AAA report.
.
https://www.m3post.com/forums/showthread.php?t=1898330
.

A very interesting report (I'll read the full report later), and whilst I certainly wouldn't want carbon buildup found in the lower tier fuels by the AAA, I don't see that causing hesitation. Power loss I could certainly see happening though, with it restricting air flow somewhat. And pinging if it happened inside the cylinders (assuming knock control couldn't stop it).

I wish the AA or RAC had done a similar test on UK fuels!
Are the same labelled fuels the same constituents in the US and UK??

Originally Posted by Space Horse

Unfortunately for me in the US, the octane supplied in gas stations varies at what altitude they are. Since Octane in fuel is usually only for compression, and when you are at higher altitude you don't need the same octane to reach the desired compression due to the air being thinner. So, the entire State of Colorado has 85-AKI, 87-AKI, and 91-AKI. It is incredibly hard to find anything higher than 91-AKI in my state or really any State that is higher than 4500 feet. Once you are in a lower altitude State then the pumps go to 87-AKI, 91-AKI, and 93-AKI.

There is also the argument that since the tune is at a certain octane and compression, that increasing octane won't necessarily do much. I don't exactly agree with that. I would definitely use higher octane if I could.

It is funny I have rented cars in the UK; I should know that your fuel is different.

What is the mileage of your car? That can definitely rule in/out whether carbon build up is a concern.

Also, what RPM are you usually at when cruising on the Highway? For how rich these cars run stock IMO (My SC tune makes it worse) unburnt fuel over long periods of not higher revs (3000+) will definitely start clogging things up.

These cars also have pretty aggressive camshafts. Have you checked the Camshaft or Crankshaft position sensors? My friend had an XJ Cherokee (Jeep) that had a camshaft sensor go bad which made it rev terribly. (Not here to say anything Jeep makes can even hold a candle to the mechanical marvel that the s65 is)

A camshaft in the wrong place in the wrong time frame can certainly affect what will happen when you stomp the gas. That could also explain it getting worse slowly over time. These already don't typically like low revs.

With how low the revs are when this is happening, might point to the cam being offset slightly when near idle. The engines probably mechanically fixing it and adjusting it to then freely rev (Redlining 4th is awesome .)

I know it isn't possible for it to be that far off. However, engines have cam position sensors for a reason.

Re octane and altitude, ah got ya, I did see that mentioned in the wiki, I guess you have the octane you need then. Unless you travel to a lower altitude state!

My M3's done 86k miles now. Although it does very low annual mileage with me, this is not compromised of many short journeys, rather it is infrequent use but nearly all longer drives.
e.g trips to a circuit, a trip to the Nurburgring each year (but bar once, not on it ), country drives typically lasting between 2-3+hrs (on Sunday I went for a 3 hr spin). So combined with doing 2 track days a year (so far, would like to do 3 at least!) I think this usage would keep carbon deposits low.
Also, as I said just above, I don't see how carbon deposits would cause hesitation, but I'm all ears if I've missed something there!

Re cam sensor, well aside from no fault codes, it starts fine (a symptom of one of those going bandy) and revs just fine too, right upto the redline (which in 4th is indeed fun btw! ).
And it runs fine at low revs, although I don't normally cruise at less than 2k RPM, it will pull fine from 1500 RPM. Unless I snap open the the throttle at less than 1500, which is normally in 1st gear, sometimes 2nd. Then it hesitates for a second, and actually when it did it once on my sunday drive, it actually misfired for that second or 2 this time!
Oh, and on highways I typically do 70-80 in 6th, whatever revs that is.

Originally Posted by Scrippy

I see all the typical ideas being brought up and I agree with them. I’ve had idle problems like hunting and stalling before and a new fuel vent valve fixed it.
I’ve also had 1 of 2 TA’s fail (120,000ish miles) and prior to it failing I had idle issues like hunting, stalling and hesitation with gentle throttle application from a stop. Just this week my final OE TA failed (281,000) and I had idle hunting, stalling and hesitation with gentle throttle application from a stop. I finally got a code for bank 1 TA. I’ve opened both of the failed TA’s and the first 5-7 teeth are worn. This is the start range where the TA wakes on ignition and opens the throttles for start and idle. So I will bet you have 1 or both TA’s shitting the bed on ya. Good luck.

No idle or hunting problems here, just the hesitation at low revs and quickly opening the throttle.
Wow that's got to be a record mileage for an OEM TA! lol.
As per my op, mine were changed for rebuild ones a couple of months before I got it, so have done about 12k miles. I think it would be very unlikely they've gone already....

Originally Posted by tdott

What tune are you on?

I've seen certain tunes that did not throw a check engine light, but as soon as stock 240E/241E was flashed back, there was a CEL and misfire code that led to a bad coil causing a slight hesitation/shudder at low rpm. Sounds like it might be similar to your issue.

It's on the standard tune/map AFAIK (as per the op), I guess I could check with ISTA?
I mentioned in my reply to Space Horse above, that for the first time it actually misfired during a hesitation 'event' on Sunday.
Thinking about it, I've had this kind of problem on other cars at work, and coils/plugs is a common cause! And often won't give a fault code where the misfire is brief!

I think what I'll do is check for air/vac leaks, and if I don't find any I'll change the plugs first (even though they've only done 25k miles). Then see how it goes.

[spammysammich]

How old are your injectors?

[Assimilator1]

Originally Posted by spammysammich

How old are your injectors?

Original AFAIK (86k miles, 2008)

[Assimilator1]

Thought I'd quote Richbot here from another thread as it's very relevant, and also I'd forgotten about his reply to me over 1 year ago!

Originally Posted by Richbot

Depends on age and mileage obviously. The coils in my car were about 8 years old and 80,000 miles old when I changed them, and I'm at 142,000 miles and 16 years old now. Mostly for me it was about servicability - the old coils were getting brittle and stiff. They get hot, and are plastic, and you have to yank hard on them to get them on and off. You can always keep the old ones as spares or rotate a couple newer ones to the back of the engine bay.

I noticed a pretty big difference in part throttle/transient response on new plugs after the plugs get above 20k miles back when I let that happen, so I stopped letting that happen, and I no longer notice a difference changing at 15k. The dyno doesn't tell you everything. It's also a good excuse to check for oil leaks on the valve cover with stuff out of the way

I'm one of the ever-diminishing number of people on here who have owned their car since it was new. Please be kind to me in my old age.

[spammysammich]

Given how few miles you put on the car and the age and the fact that the injectors are known to scrap these motors, I would change the injectors and plan on checking them every now and then by running the misfire detection ABL in ISTA to monitor combustion quality.

[Assimilator1]

As per the op, I did a combustion quality check a few weeks ago, it was well within spec.

Yea injectors is an ongoing open question, and one I'm still on the fence about.
Re mileage, I would've thought higher mileage cars would be at greater risk than lower mileage ones?

[spammysammich]

I’m of the opinion that cars that are driven more often suffer less fuel injector degradation from ethanol than garage queens. But that’s just based off my experience with the Subaru community. More to do with time sat soaked in up to 5% ethanol fuel than mileage. Or in some cases poor quality fuel.

[Assimilator1]

Ah got ya, fair enough.
Although I'm going to exhaust other options first before looking at injectors (vac leaks, plugs, etc).

[Assimilator1]

Thought I should update this thread, I recently replaced the plugs and injectors (@88.4k miles).
But before I put in the new injectors I tested for the hesitation, it pretty much disappeared after replacing just the plugs.
And since then I have driven it a bit too, I'd say at the least the hesitation is 95% gone, there's just maybe the occasional very slight hint of it left.

PS. Old plugs had done 27k miles.
Back of inlet valves were literally shiny clean