RPM drops on idle

[SCL_///M3]

Hi All,

This thing has been bugging me for quite some times now, that whenever I bring the car to a full stop and leave my foot on the brake, the RPM stays at around 750-800rpm for a second then starts to drop and settles at 500-550rpm, at which point I can feel a slight vibration through the steering wheel. If I lift my foot from the brake the PRM climbs back to 750-800rpm (will drop back to 500-550 when the brake is re-applied). The only time this does not happen is when I have the AC on.
I have brought the car to my dealership and the tech told me that they couldn't find anything wrong with it, as the car does not throw any error code nor did they find any error code when they scanned the ECU.
I believe the normal idle speed for e92 M3s should be around 750 rpm, right?
Has anyone else experienced the same symptom? Any solutions?
Btw, mine is a 2010 DCT. I have done the DCT software update back in 2011 (there was a recall on the software).
Also, do you guys usually leave your foot on the brake at stoplights?

Thanks.

[CrusherM3]

Originally Posted by SCL_///M3

Hi All,

This thing has been bugging me for quite some times now, that whenever I bring the car to a full stop and leave my foot on the brake, the RPM stays at around 750-800rpm for a second then starts to drop and settles at 500-550rpm, at which point I can feel a slight vibration through the steering wheel. If I lift my foot from the brake the PRM climbs back to 750-800rpm (will drop back to 500-550 when the brake is re-applied). The only time this does not happen is when I have the AC on.
I have brought the car to my dealership and the tech told me that they couldn't find anything wrong with it, as the car does not throw any error code nor did they find any error code when they scanned the ECU.
I believe the normal idle speed for e92 M3s should be around 750 rpm, right?
Has anyone else experienced the same symptom? Any solutions?
Btw, mine is a 2010 DCT. I have done the DCT software update back in 2011 (there was a recall on the software).
Also, do you guys usually leave your foot on the brake at stoplights?

Thanks.

Usually always have foot on the at brake stoplights...Hold over habit from driving regular automatics in the past.

No problems with idle...but mine is barely just a little over a month old. GL with a fix.

BTW...I have DCT also.

[VCP]

Get them to check the vacuum brake booster might be leaking when you have your foot on the brake and causing a big vacuum leak that's dropping your idle. Try idling and pumping your brakes and see if the idle is any worst.

[SCL_///M3]

Originally Posted by VCMperformance

Get them to check the vacuum brake booster might be leaking when you have your foot on the brake and causing a big vacuum leak that's dropping your idle. Try idling and pumping your brakes and see if the idle is any worst.

Thanks for the advice. But if there is a vacuum leak shouldn't it throw some kind of error code?

[Race_Doc11]

I have the same exact problem. I took it to 2 dealers and both claim the car is fine (no codes)!!! One dealer reprogrammed the car but it didn't fix the problem...
there is a thread on this but with no answer:
http://www.m3post.com/forums/showthread.php?t=395846

one guy claimed his car has done the same but it returned to normal after that!!!! In my case it is still doing it regardless the fuel I'm using.

Originally Posted by SCL_///M3

Hi All,

This thing has been bugging me for quite some times now, that whenever I bring the car to a full stop and leave my foot on the brake, the RPM stays at around 750-800rpm for a second then starts to drop and settles at 500-550rpm, at which point I can feel a slight vibration through the steering wheel. If I lift my foot from the brake the PRM climbs back to 750-800rpm (will drop back to 500-550 when the brake is re-applied). The only time this does not happen is when I have the AC on.
I have brought the car to my dealership and the tech told me that they couldn't find anything wrong with it, as the car does not throw any error code nor did they find any error code when they scanned the ECU.
I believe the normal idle speed for e92 M3s should be around 750 rpm, right?
Has anyone else experienced the same symptom? Any solutions?
Btw, mine is a 2010 DCT. I have done the DCT software update back in 2011 (there was a recall on the software).
Also, do you guys usually leave your foot on the brake at stoplights?

Thanks.

[jeremyr4]

Did any of you guys ever come up with a resolution to this problem? I'm asking because I have a 2013 E93 M3 with around 400 miles and I am having this problem. I am idling right around 500-550 and the car is shaking. Not sure if it makes a difference but my car is a DCT and is stock.

Thanks for everyone's help,
Jeremy

[BPMSport]

It definitely should not do that. Jeremy, I'm happy to check the car out if you bring it by.

[jeremyr4]

Originally Posted by Mike Benvo

It definitely should not do that. Jeremy, I'm happy to check the car out if you bring it by.

Thanks Mike - I appreciate it. I might take you up on that. Trying to get through another 350 miles or so until my 1,200 mile service before I deal with it, unless it stalls (which it hasn't yet!).

BTW, off topic, I heard an OEM Exhaust Mod (non-perforated) today and I decided I'm going with it - after my 1,200 mile service. Thanks for your help!

[elm3]

Originally Posted by VCMperformance

Get them to check the vacuum brake booster might be leaking when you have your foot on the brake and causing a big vacuum leak that's dropping your idle. Try idling and pumping your brakes and see if the idle is any worst.

+1, main culprit is the brake booster. They can do a vacuum test and see if the booster is holding vacuum.

[ecalcagnino]

Mine does this also. I went to the dealer for something else a couple weeks ago and they said it was normal as well. Not so sure about that.

Mine has an added weirdness - if the AC or heat is on, it will not drop RPMs. Anyone else confirm?

2011 DCT

E

[jeremyr4]

Originally Posted by ecalcagnino

Mine does this also. I went to the dealer for something else a couple weeks ago and they said it was normal as well. Not so sure about that.

Mine has an added weirdness - if the AC or heat is on, it will not drop RPMs. Anyone else confirm?

2011 DCT

E

Precisely the exact symptoms as my 2013 E93 M3 with DCT. I have read a number of threads on this and our symptoms are all identical. With AC on my idle is about 750 - nice and smooth.

I have not tried to check my break pedal (per the suggestion in the previous replies) but I will give that a shot in the next couple of days. For now, as long as the car doesn't start stalling I will probably wait another 1-2 months until my 1,200 mile break-in to see what my dealer says...

There is NO way this is normal. I was just in a 2011.5 E93 M3 with DCT yesterday that was idling at around 600-700 - very smooth. There is just no way our $80k cars were designed to shake at idle - my mirror shakes!

Let's keep each other updated, as I'm sure someone will figure this out. Thanks for everyone's help!

[jeremyr4]

Originally Posted by elm3

+1, main culprit is the brake booster. They can do a vacuum test and see if the booster is holding vacuum.

Thanks very much - I will give this a shot. Hopefully it will be that simple!

[ecalcagnino]

Please post back here with results. Subscribed. Thanks!

[jeremyr4]

I tested the vacuum booster theory today and here's the consistent behavior of my car (I have a 2013 E93 M3 w/DCT):

Idle in 1st (stopped) with foot on brake - 500-550 RPMs + some shaking
Idle in 1st (stopped) with foot on brake w/AC on - 700-750 RPMs + perfectly smooth

Take foot off of brake while idle in 1st - Within 1 second RPMs jump back up to 700-750 + perfectly smooth - Where it probably should be the whole time! If I put my foot back on the break then the RPMs will gradually drop (in 2-3 subtle stages) to 500-550 RPMs within 3-5 seconds.

So there is a clear correlation for me - No A/C in idle in 1st (stopped) - Foot on break brings the RPMs down to 500-550 with shaking. Foot off brake brings idle back up to 700-750 + perfectly smooth.

Does this sound like the vacuum booster that was mentioned earlier? If yes then perhaps that's the problem everyone in this thread is experiencing?

Note: Unfortunately I did not test the car in neutral. But presumably the DCT is in neutral (ie. clutch NOT engaged) if it says 1 but is stopped and my foot is not on the brake! So I'm guessing being in N will yield the same results.

Thanks for everyone's help,
Jeremy

[amyoescobar]

Try idling and pumping your brakes and see if the idle is any worst.

[jeremyr4]

Originally Posted by amyoescobar

Try idling and pumping your brakes and see if the idle is any worst.

I did try that a couple of times but it didn't do much. But only pumped the brakes a few times. What do you think based on my symptoms above? Thanks for your help.

[elm3]

I still think that it is your brake booster. Still under warranty, take it and let them do some tests to your car, since the problem can obviously be re-created. Once they figure out what it is, they'll replace whatever it is that is faulty. Hope that you'll get it fixed soon.

[jeremyr4]

Originally Posted by elm3

I still think that it is your brake booster. Still under warranty, take it and let them do some tests to your car, since the problem can obviously be re-created. Once they figure out what it is, they'll replace whatever it is that is faulty. Hope that you'll get it fixed soon.

Ok - thanks. My concern is that a couple others on the Board have had this problem for months and they haven't been able to find the problem. Thanks again for your help.

I will post an update for everyone after I take my car in. Unfortunately I don't anticipate bringing it in for a little while (I am still 350 miles away from my 1,200 mile service, which will probably take me 1-2 months to drive). If anyone else figures it out please post an update - thanks very much.

[M3PO]

I think it's related to the brake booster also. The AC is bumping the idle a bit (due to the extra load with the compressor on) and that is probably enough to mask the problem.

[jeremyr4]

Quick update for anyone following this thread. I did a little more testing and here's what I found: With the car stopped in P or 1 - If I have my foot on my brake firmly planted down then my RPMs dip to the 500-550 range + shaking. BUT - If I have my foot more softly planted on my brake (not off the brake but not all the way down and with less force so it's floating above the fully down mark) then I can get the RPMs to be more in the 600-700 range.

In other words, there seems to be a direct correlation between my brakes and my RPMs (ie. brakes fully engaged and firmly planted = 500-550 range, no brakes = normal 700-750 RPMs, partial brakes or partial brake force = 600-700 RPMs). So there seems to be a clear relationship with my brakes, which means the brake vacuum booster is highly likely the cause as a couple people have suggested.

Sorry if this seems obvious but I thought it might help the others who are trying to figure out the cause for themselves. If you are trying to figure out this problem on your car then I would suggest trying various brake pressures at full stop to see if you end up with the same results as me. If that's the case then it's likely your brake vacuum booster...

As I have mentioned before, I'm not taking my car in until my 1,200 mile service, which is now 320 miles away and counting. I will probably take mine in around mid-late Nov at my current pace...

Hope that helps,
Jeremy

[Race_Doc11]

Same here! I even learned to ease on the brake when it happens....

Originally Posted by jeremyr4

Quick update for anyone following this thread. I did a little more testing and here's what I found: With the car stopped in P or 1 - If I have my foot on my brake firmly planted down then my RPMs dip to the 500-550 range + shaking. BUT - If I have my foot more softly planted on my brake (not off the brake but not all the way down and with less force so it's floating above the fully down mark) then I can get the RPMs to be more in the 600-700 range.

In other words, there seems to be a direct correlation between my brakes and my RPMs (ie. brakes fully engaged and firmly planted = 500-550 range, no brakes = normal 700-750 RPMs, partial brakes or partial brake force = 600-700 RPMs). So there seems to be a clear relationship with my brakes, which means the brake vacuum booster is highly likely the cause as a couple people have suggested.

Sorry if this seems obvious but I thought it might help the others who are trying to figure out the cause for themselves. If you are trying to figure out this problem on your car then I would suggest trying various brake pressures at full stop to see if you end up with the same results as me. If that's the case then it's likely your brake vacuum booster...

As I have mentioned before, I'm not taking my car in until my 1,200 mile service, which is now 320 miles away and counting. I will probably take mine in around mid-late Nov at my current pace...

Hope that helps,
Jeremy

[CanAutM3]

Originally Posted by jeremyr4

Quick update for anyone following this thread. I did a little more testing and here's what I found: With the car stopped in P or 1 - If I have my foot on my brake firmly planted down then my RPMs dip to the 500-550 range + shaking. BUT - If I have my foot more softly planted on my brake (not off the brake but not all the way down and with less force so it's floating above the fully down mark) then I can get the RPMs to be more in the 600-700 range.

In other words, there seems to be a direct correlation between my brakes and my RPMs (ie. brakes fully engaged and firmly planted = 500-550 range, no brakes = normal 700-750 RPMs, partial brakes or partial brake force = 600-700 RPMs). So there seems to be a clear relationship with my brakes, which means the brake vacuum booster is highly likely the cause as a couple people have suggested.

Sorry if this seems obvious but I thought it might help the others who are trying to figure out the cause for themselves. If you are trying to figure out this problem on your car then I would suggest trying various brake pressures at full stop to see if you end up with the same results as me. If that's the case then it's likely your brake vacuum booster...

As I have mentioned before, I'm not taking my car in until my 1,200 mile service, which is now 320 miles away and counting. I will probably take mine in around mid-late Nov at my current pace...

Hope that helps,
Jeremy

I have started to see the exact same symptoms on my car. It also coincides with the car going in limp mode once in a while. I don't know if it is related though. The car is now out of warranty, I hope it won't cost a fortune to fix...