[Solved] More problems :(

[romemmy]

Hi all,

I got the vacuum sensor fixed (P1209 code), and all seems good. Driving all day, no more codes..

However, now I'm getting a weird other issue. Sometimes (and only sometimes) I will have very little power until about 3Krpm, and then all the power comes (feels like a really laggy turbo!). The power loss feels like when traction control reduces power, but of course there is no traction control issue here. I could have my foot to the floor and the revs climb really slowly, until eventually all the power arrives.

There are no codes, my data logger says fuel pressure isn't abnormal (50-65psi), and no abnormal vibrations or noises. Cruising above 3Krpm, everything is as responsive as normal.

Typically the issue starts occurring after driving for at least several minutes. Initially there is no issue at all.

I see posts about VANOS possibly being an issue, but typically that's on much higher mileage cars (this one only has 44Kmiles). I guess fuel filter, injectors, MAF, etc, could be causing it, but I would have expected either the problem consistently or issues to be seen higher up the rev range.

As part of the vacuum pipe replacement I had to remove the brake master cylinder, but I don't see how that could be affecting power delivery..

On an unrelated note, my TPMS seems to have failed too. I reset it, then it tells me low pressure within minutes. All the pressures are fine and are not fluctuating. TPMS is not even telling me which tire is low - they all highlight yellow! Had tires replaced a few weeks ago, but this problem started about a week ago.

Any ideas would be appreciated!

Thanks!

S.

[romemmy]

Hi all,

More info...

1) when the problem occurs, it's consistent. Turning the car off then on again immediately, the issue goes away until the next time it happens.

2) the car is barely able to make it up a hill when the issue is present. The revs build then fall off - it simply doesn't have enough power.

3) from standstill if I try to accelerate quickly, the car briefly (half a second) responds normally, then the revs crash down and build slowly

4) I data logged the car while it was happening. The accelerator pedal position shows as wide open, but suspiciously the absolute throttle (i.e. what the throttle bodies are doing) doesn't change until the revs finally build up. When the issue isn't there I'll see absolute throttle at >60% when accelerating from stand still.

Basically I think the data is showing that the DME itself is basically limiting power - but it's doing it without a code or reporting any issue!

Any ideas? I'm supposed to be at Sonoma Raceway in the morning so this is extremely frustrating

Thanks!

S.

[kawstik]

The obvious, and my guess would be an intake/vacuum leak. It seems trivial but the smallest of leaks can rob hp like a klepto on a free for all.

[romemmy]

Thanks kawstik! I thought about that, but if there were an air system leak, wouldn't it throw a code? Also, based on the data, the ECU seems definitely responsible for the power loss (especially as just restarting the car causes the issue to immediately go away).. A leak I would imaging would be more consistent, affect more of the power range, and would typically always be present? The puzzling part for me is how the ECU could do anything without an associated code..

Thanks!

S.

[romemmy]

Hi all,

Any more ideas? The issue is still consistent (after a few miles of driving, coming to a stop and trying to drive off will have virtually no power until 3-4Krpm, problem goes away when you turn off and turn on the car until it happens again a few miles later). I can get going from standstill "relatively" normally if I rev to 3Krpm then lift the clutch quickly (basically almost launching, but not quite).

I am trying to get hold of a working INPA cable quickly (I ordered one and it ended up being the white PCB and didn't work). Hopefully I can do more direct diagnostics then, but until then, any ideas would be appreciated. I even spoke with an ex-Dinan engineer, and he was stumped too! He thought maybe someone in the past (before I owned the car) had flashed the ECU with some new map that is malfunctioning now.

Anyway, I will keep this thread updated as I find the issue.

Thanks!

S.

[Amirsm3]

Take it to a dealership. Their code readers are much more descriptive and thats how they found my vacuum sensor failure as opposed to the throttle actuator failure that my buddy's code reader initially reported.

[romemmy]

Originally Posted by Amirsm3

Take it to a dealership. Their code readers are much more descriptive and thats how they found my vacuum sensor failure as opposed to the throttle actuator failure that my buddy's code reader initially reported.

Hi Amirsm,

Thanks for the response! I'd rather not take it to the dealership though. From what I've seen so far that response is FAR more common on M3 forums than I expected (Porsche, Lotus, Evo, GT-R, etc, forums almost never respond with that) . Once I have the cable I will be able to do a deeper analysis, but I wanted to see if anyone had encountered the issue before, or had some M3-specific diagnostic steps (since I'm just getting familiar with the M3). I also had the pressure sensor issue, but was able to diagnose and replace it without too much trouble. The issue here is that there are no codes being thrown at all!

When I find the issue I will post back to the forum so at least this knowledge will be out there.

Thanks!

S.

[stylelab]

I have a similar issue with my car. I brought it to the dealer and they replaced a vaccum pump related to the brakes. It didn't resolve the issue. I need to bring it back. Everything started happening because I thought it was due to bad gas. I got several codes (emission issues, low power etc). It really sucks. Let me know what you find out. My next dealer appointment is early July so any additional info you may find out would help. Good luck. Thanks.

[romemmy]

Originally Posted by stylelab

I have a similar issue with my car. I brought it to the dealer and they replaced a vaccum pump related to the brakes. It didn't resolve the issue. I need to bring it back. Everything started happening because I thought it was due to bad gas. I got several codes (emission issues, low power etc). It really sucks. Let me know what you find out. My next dealer appointment is early July so any additional info you may find out would help. Good luck. Thanks.

Hi stylelab,

Do you happen to know which codes got thrown? Did the dealer also replace the actual vacuum sensor (it comes as part of a 3-way pipe assembly)?

Thanks!

S.

[stylelab]

I'm traveling now so I don't have the dealer invoice for the repairs. I'll try and see if i can get access to it and report back.

[elusive303]

+1 to what romemmy said.

I had the same issue p1209 over the last few week. I had the vacuum sensor replaced last week and the car is back to normal.

It comes as a full assembly as romemmy described. My mechanic charge me $158 for the part and an hour of labor for install.

Originally Posted by romemmy

Hi stylelab,

Do you happen to know which codes got thrown? Did the dealer also replace the actual vacuum sensor (it comes as part of a 3-way pipe assembly)?

Thanks!

S.

Originally Posted by stylelab

I'm traveling now so I don't have the dealer invoice for the repairs. I'll try and see if i can get access to it and report back.

[thugmaster]

Originally Posted by romemmy

Hi all,

I got the vacuum sensor fixed (P1209 code), and all seems good. Driving all day, no more codes..

However, now I'm getting a weird other issue. Sometimes (and only sometimes) I will have very little power until about 3Krpm, and then all the power comes (feels like a really laggy turbo!). The power loss feels like when traction control reduces power, but of course there is no traction control issue here. I could have my foot to the floor and the revs climb really slowly, until eventually all the power arrives.

There are no codes, my data logger says fuel pressure isn't abnormal (50-65psi), and no abnormal vibrations or noises. Cruising above 3Krpm, everything is as responsive as normal.

Typically the issue starts occurring after driving for at least several minutes. Initially there is no issue at all.

I see posts about VANOS possibly being an issue, but typically that's on much higher mileage cars (this one only has 44Kmiles). I guess fuel filter, injectors, MAF, etc, could be causing it, but I would have expected either the problem consistently or issues to be seen higher up the rev range.

As part of the vacuum pipe replacement I had to remove the brake master cylinder, but I don't see how that could be affecting power delivery..

On an unrelated note, my TPMS seems to have failed too. I reset it, then it tells me low pressure within minutes. All the pressures are fine and are not fluctuating. TPMS is not even telling me which tire is low - they all highlight yellow! Had tires replaced a few weeks ago, but this problem started about a week ago.

Any ideas would be appreciated!

Thanks!

S.

My car had similar lag issues. Turns out both my throttle actuators were going bad. Also one of the wires connecting the actuator was burnt off due to heat. After I changed them and replaced the wire, car felt great again.

[romemmy]

Originally Posted by thugmaster

My car had similar lag issues. Turns out both my throttle actuators were going bad. Also one of the wires connecting the actuator was burnt off due to heat. After I changed them and replaced the wire, car felt great again.

Hi thugmaster,

Did you get any associated codes? Usually I've found people with throttle actuator issues get TPS-related codes (because the ECU requests, say, 60% - but the potentiometers show only 15% actual - causing an error state). In my case my actual throttle shows about 14% when the pedal position is >80% - both values are seen by the ECU (when the problem isn't there, throttles open >65%).

However, if you weren't getting codes, then that would be weird (like mine).

I plan on removing the plenum tomorrow to take a look at the throttles, just in case there is something obvious. I will also be measuring vacuum directly to ensure there aren't any crazy anomalies.

Thanks!

S.

[romemmy]

I fixed a problem today, and I wonder if it might be the cause of this reduced power issue... My wife was driving the car today and a helpful person drove up next to her and told her that the brake lights weren't turning off on the M3! A difficult to notice issue since we can't see the back of the car when driving...

When I fixed the vacuum pipe, I did take off the cover under the steering and disconnected the pedal from the booster. Since it wasn't actually necessary, I put it all back together not noticing that I had knocked the hall effect sensor that detects if the pedal has been depressed. This moved the sensor out by about half an inch, meaning that the car would intermittently detect the pedal return - so the lights would be on all the time sometimes (mostly apparently staying on).

I fixed the problem by just pushing the sensor back in to its fitting so it clicked back in to place, but I wonder now if this will fix the reduced power issue. I know that the DSC uses the brake sensor as part of its operation, and I've seen reports that the DSC will throw errors (and reduce power) that aren't seen by a code scanner. I actually have a Carly (which hopefully can see these hidden codes like they claim) coming tomorrow, so maybe I'll see historical codes (hopefully).

I will be taking a long drive later today, so will know for sure if it's fixed - and if so it will all make sense as to why it started happening after fixing the vacuum sensor.

Thanks!

S.

[romemmy]

So far so good. Several drive cycles and it hasn't happened again!

Seems that the issue that felt like the DSC reducing power was actually the DSC reducing power due to the brake pedal sensor not detecting the pedal return. Kind of crazy why this wasn't thrown as a regular code. If it really is thrown as a hidden code, that is purely a money making tactic for BMW dealers (I'll check the DME later today).

Thanks!

S.

[romemmy]

I finally got my Carly and confirmed that the DME had several hidden codes, one of which was the brake light switch malfunction, which caused the random reduction of power under 3Krpm.

Thanks!

S.

[monterey]

Good job

[mharris2007]

Originally Posted by monterey

Good job

Man that sounds painful. Nice work.

[thugmaster]

Originally Posted by thugmaster

My car had similar lag issues. Turns out both my throttle actuators were going bad. Also one of the wires connecting the actuator was burnt off due to heat. After I changed them and replaced the wire, car felt great again.

Hey sorry for the late reply. I didn't get the codes but these were the malfunctions on my I drive. Common for a bad throttle valve. Hope this helps