Cold start - rev bouncing, no misfires or CEL

A6 All/ S6 All
#1

Hi all,

I have had my '07 S6 for a few years now and just recently have noticed it doing this rev bouncing thing during a cold start once the car has been sitting for a while.

During the cold start routine the revs bounce up about 300-500 rpm at roughly half-second intervals. If I press the gas pedal a bit, it revs fine, but goes right back to bouncing after I take my foot off the pedal. There are no misfires and a VAG-COM scan shows no active CEL.

Once the cold start routine is done, the revs are rock solid and car runs great. Also, if I immediately shift the car into drive after starting it, the rev bouncing stops.

I did have the car smoke tested not long before this started due a CEL that indicated an air leak. We did find some leaks but all of them were repaired except for a very small one seen at the intake manifold (between the upper and lower sections) and this cleared the CEL which hasn’t returned for months. However, now I’m getting this rev bounce thing…

Would a small air leak cause something like this? Anything else I should be checking?

Thank you!

#2

Well it could be a ton of things. But on cold start the car is not using the MAF readings and also not taking in feedback from the 02s yet.

Depending on how long sitting for a while is your cars ECU will not have trimmed up for environmental conditions and the car is just trying to keep the rpms within range. I would consider this normal. Also depending on the outside temps the cars SAI system could have been running. That will make idle situations more likely to swing greater amounts.

#3

Thanks for the reply justincredible!

The car is garaged the vast majority of time and I usually don’t drive it much in the winter so it sometimes sits for long periods (stored properly though on a battery tender, fuel stabilizer, tire flat spot prevention, etc…). It does seem to take the car sitting for a week or longer before the rev bouncing shows up though.

I was worried it was indicative of something bad but sounds like I shouldn’t be too worried. Thanks again for the info, love this forum!