Inconsistent Idle

Hello all.

I've noticed on a handful of occasions where my car will dip down in RPMs when I'm sitting at a red light. The car drives fine with no abnormalities, but every once in a while after coming to a stop, it will drop to 500 and maybe a little less and then it will bounce back up to about 800 and continue this pattern until I drive off. I have even had it drop low enough where it stalled the car once.

Again, this is inconsistent and random when this will happen. Just got done driving 20 miles @ 80 mph on the highway? Sometimes it will dip at the light, sometimes it is a flat and level 800 RPM. Little hard driving in the mountains? Who knows what it will do! It is infrequent as well.

It doesn't really seem like it's much of an issue with no codes or lights showing up, but it is odd. My big concern is any additional load it is putting on the engine at these low revolution speeds. I changed out my plugs trying to give that a go, but the results are the same. Has anyone seen this before? Not sure if these are MAF cars, but is it possible something like that is dirty?

2011.75 E90 M3 6MT

Thanks!
Tyler

Have you checked your idle control valve?

As stated above, idle control valve is the likely culprit as per research on this forum. I have seen this issue in my car a few times, but only when filling up at random gas stations while traveling. It hasn't happened since I have mostly stuck with the two or three BP stations in my neighborhood.

Hey mate,

No MAF on these, MAP only.
Pull any stored codes and freeze frames first and see if you have any hints there but it certainly sound like the beginning of the end for the ICV unfortunately. Not uncommon on these cars.
I have heard of some guys pulling the ICV and giving them a clean out with upper engine cleaner or similar with some success but if it's the PCB it's time for a new one.
Pretty easy DIY, may as well do the throttle valve actuators whilst you under there as they WILL break

Hope this helps,
Craig

Thanks for everyone's input. Looks like I'll have to give the idle control valve a look-see. Is this an easy inspection/change out?

OzCraig wrote

Hey mate,

No MAF on these, MAP only.
Pull any stored codes and freeze frames first and see if you have any hints there but it certainly sound like the beginning of the end for the ICV unfortunately. Not uncommon on these cars.
I have heard of some guys pulling the ICV and giving them a clean out with upper engine cleaner or similar with some success but if it's the PCB it's time for a new one.
Pretty easy DIY, may as well do the throttle valve actuators whilst you under there as they WILL break

Hope this helps,
Craig

I'm terrible with acronyms. Any hints towards what PCB is? I think I figured out the rest of 'em

Any chance the stalls happen after filling the gas tank?

spazzyfry123 wrote

Thanks for everyone's input. Looks like I'll have to give the idle control valve a look-see. Is this an easy inspection/change out?

I'm terrible with acronyms. Any hints towards what PCB is? I think I figured out the rest of 'em

Hey mate,

It isn't a mech job, definitely a DIY if you've spun spanners before.
You need to take the airbox out, plenum off, disconnect the TVA's, Vanos etc plugs, then you have access to it. If you get to that point I would change out the TVA's with some from Jason at Rebuild.org.uk, saves you doing them later as they WILL break.

Printed Circuit Board - More specifically the components burn out/die. At that point you are need to replace the whole unit.

Hope this helps
Craig

spazzyfry123 wrote

Hello all.

I've noticed on a handful of occasions where my car will dip down in RPMs when I'm sitting at a red light. The car drives fine with no abnormalities, but every once in a while after coming to a stop, it will drop to 500 and maybe a little less and then it will bounce back up to about 800 and continue this pattern until I drive off. I have even had it drop low enough where it stalled the car once.

Again, this is inconsistent and random when this will happen. Just got done driving 20 miles @ 80 mph on the highway? Sometimes it will dip at the light, sometimes it is a flat and level 800 RPM. Little hard driving in the mountains? Who knows what it will do! It is infrequent as well.

It doesn't really seem like it's much of an issue with no codes or lights showing up, but it is odd. My big concern is any additional load it is putting on the engine at these low revolution speeds. I changed out my plugs trying to give that a go, but the results are the same. Has anyone seen this before? Not sure if these are MAF cars, but is it possible something like that is dirty?

2011.75 E90 M3 6MT

Thanks!
Tyler

Fuel tank breather

http://www.m3post.com/forums/showthread.php?t=1273927

TurboPR wrote

Fuel tank breather

http://www.m3post.com/forums/showthread.php?t=1273927

Very interesting! The video depicts very similar results to mine, but I can't really say that I notice it after a fill up necessarily. It's a shame that Photobucket removed all the photos for that DIY.

I will say that after a fill up I drove around with no issues. Stopped at a store after some driving, came back out, and the service engine light came on. I ran the code and it had to do with evap (so either the secondary canister or the fuel cap is what I would point it at). I had probably 3/4 tank in the car when I dropped it off at my local shop for some work to be done and we cleared the code to see if it popped back up again. Drove the entirety of the tank with no issues. Filled up and drove around for a while. Same deal...parked the car after some driving with no lights, but came back out and the light came back on.

Do you think that replacing the cap could possibly alleviate my idle issues as well?

I just had this happen to me after a service on Friday. Does your idle dip regardless of if your in P, N or gear? I have a 2012 DCT, so it's interesting to see this affects both manual and DCT cars. By chance, is your brake pedal soft/spongy at all? I'm trying to determine if this could be the idle control valve or brake booster losing vacuum. I haven't stalled yet because of this, but I know my car didn't do this prior to my service, which was just an oil change and battery replacement.

OzCoE92 wrote

I just had this happen to me after a service on Friday. Does your idle dip regardless of if your in P, N or gear? I have a 2012 DCT, so it's interesting to see this affects both manual and DCT cars. By chance, is your brake pedal soft/spongy at all? I'm trying to determine if this could be the idle control valve or brake booster losing vacuum. I haven't stalled yet because of this, but I know my car didn't do this prior to my service, which was just an oil change and battery replacement.

Mine is a manual. The brakes feel great since I just had my pads and fluids changed out. But this problem was going on before that service and still continuing now. Took it out for a ride during lunch today and it was a steady, even 550ish RPM and never bounced or dipped. Pulled it out of the garage last night to fill it up for today and it was bouncing on my way to the station and on my way home after filling up. It's very random.

It's very odd that this problem happens randomly. If I am remembering correctly, I thought the factory idle was 750 rpms or close to that. I have been seeing 500-550 rpms since last Friday.

spazzyfry123 wrote

Very interesting! The video depicts very similar results to mine, but I can't really say that I notice it after a fill up necessarily. It's a shame that Photobucket removed all the photos for that DIY.

I will say that after a fill up I drove around with no issues. Stopped at a store after some driving, came back out, and the service engine light came on. I ran the code and it had to do with evap (so either the secondary canister or the fuel cap is what I would point it at). I had probably 3/4 tank in the car when I dropped it off at my local shop for some work to be done and we cleared the code to see if it popped back up again. Drove the entirety of the tank with no issues. Filled up and drove around for a while. Same deal...parked the car after some driving with no lights, but came back out and the light came back on.

Do you think that replacing the cap could possibly alleviate my idle issues as well?

This is a big clue as to where your problem is coming from, the Evap system acting up will cause the exact problem you described. Sounds like a vent valve for sure...

+1 for TurboPR

HerbNRacer wrote

This is a big clue as to where your problem is coming from, the Evap system acting up will cause the exact problem you described. Sounds like a vent valve for sure...

+1 for TurboPR

+1 indeed.

If we're having to pop off the plenum off and all, might as well change out the throttle actuators and the idle control valve while we're at it.

And this is why my '71 Honda CB is in a million pieces. "Well since I have this off, I might as well do this......"

Mine does the exact same thing, wasnt sure if normal operation. I seem to notice it more when im at a stop light with my foot on the brake but if i lift off the brake and im still stationary the idle seems to go up to about 7-750. Intermittent issue for sure and no faults stored.

E92_TYLER wrote

Mine does the exact same thing, wasnt sure if normal operation. I seem to notice it more when im at a stop light with my foot on the brake but if i lift off the brake and im still stationary the idle seems to go up to about 7-750. Intermittent issue for sure and no faults stored.

With mine being a manual, the revs rise once I push in the clutch at the stop light. Not sure if the motor is raising revs in anticipation or if there is less load on the motor now that the clutch is disengaged from the transmission instead of spinning freely attached to the transmission.

Same here, no faults.

Coming back to this. My last two (or was it three...?) tanks were exclusively Shell. No issues since.

Yea since its been a bit colder i havent noticed it (same gas).

E92_TYLER wrote

Yea since its been a bit colder i havent noticed it (same gas).

This is when the gas tank vent valve is working less and the symptoms will also be less noticeable. Your problem may return randomly and/or when the weather warms back up.

What did you figure out Tyler? Fuel tank breather valve or idle control valve? I'm getting this once in a blue on the E93 but it will actually stall. It's very rare that it does not stall if it jumps. And it will typically bounce over 1,000 rpms and then drop to zero.

BOOF-M3 wrote

What did you figure out Tyler? Fuel tank breather valve or idle control valve? I'm getting this once in a blue on the E93 but it will actually stall. It's very rare that it does not stall if it jumps. And it will typically bounce over 1,000 rpms and then drop to zero.

Nothing just yet unfortunately. Honestly since the weather has cooled down a bit, I'm not seeing it nearly as often. I will say that I filled it up last night after a short drive and the car took a second to start and then almost stalled when I left the station. I think that's more directed towards driving the car for less than 10 minutes and shutting it off only to start it back up a few minutes later.

This is going into diagnosis mode at my shop when I change over the rod bearings. Hopefully we get it fixed...cheaply

I have the Blue Driver OBD which doesn't show any issues, I just picked up the Carly so I'm hoping that might get a little more in depth and tell me if anything is happening when it occurs. I do hope it's one of the two above mentioned items though.