Cold Start Idle Oscillation

[erm324]

Figured I'd ask the following question, as its become more frequent over the past few weeks:

Upon cold start, if I throw the car into reverse and try to drive with the car still in cold start warm-up (elevated RPM), the RPM oscillates noticeably when slowing to a halt (which has caused the car to stall in once instance).

Though, if I let the car warm up for 30 seconds so that it finishes the cold-start cycle and brings the RPM down to normal, and then start driving, the car runs perfectly normal without any issues.

From experience with my N54 335, fuel system-related issues (plugs, coils, injectors, etc.) tend to cause RPM oscillation after the cold-start cycle finishes and the car is at operating RPM.

Car does not throw any codes and otherwise runs perfect in all other situations. Overall, I can avoid the issue altogether by allowing the car to warm up properly and finish the *** warm up cycle, or can replicate it by attempting to back out of my garage mid-warm up.

[Used2be]

Originally Posted by erm324

Upon cold start, if I throw the car into reverse and try to drive with the car still in cold start warm-up (elevated RPM), the RPM oscillates noticeably when slowing to a halt (which has caused the car to stall in once instance).

If your M5 has the DCT perhaps it is a clutch release situation? Maybe line pressures aren't fully up and it doesn't release properly when you brake to a stop? Just a guess of course, I haven't had this problem.

[MCarsFan]

Check coil packs

[erm324]

Yes, car is DCT.

I know the E9X had idle control valve issues that exhibited similar symptoms, but I've never heard of any M5's with the issue. Anytime I've had plug/coil/injector issues on my E92 M3 and N54 335 the car has thrown codes (usually misfire) and/or had a rough idle after the car completes its cold-start cycle (both of which do not occur in this case).

If I'm patient and give the car 20 seconds I will never experience this issue, just wanted to see if others have came across it as well.

[Spinny02]

I notice it when the wheel is almost hard over when parked.

[lunden]

Totally stock car? or does it have catless downpipes.

[erm324]

Car is completely stock other than JB4+BCM. I have not experienced the issue at all since initially posting this thread, but yet again I've given the car time to warm up.

[erm324]

Originally Posted by Spinny02

I notice it when the wheel is almost hard over when parked.

Me too. Seems as if the combination of reversing out of the garage and cutting the wheel during the cat warm-up does it.