Rough idle when cold

A6 All/ S6 All
#1

Morning everyone (or should I say, anyone, since it doesn’t look like AudiRevolution S6 forum is still being used much).

I have a 2011 Audi S6, my second S6. It has a strange idle problem that happens when the car is cold. It idles fine cold when immediately started and still in park. Then when I put it in gear, it gets very rough, lurching while my foot is still on the brake. Then, once the car warms up, the idle is completely fine both in park and in drive.

Additional info, I had an ECU and TCU upgrade from JHM Motorsports done to this car several years ago (along with a lot of other work) before this cold idle issue started to happen. I don’t drive the car much and since it goes away once the car warms up, I’ve just learned to live with it but my current mechanic thinks it has to do with the PCV valve.

An AI search says this is a known issue that has to do with:

Normal catalyst-heating behavior (most likely) is still the leading explanation. The TSB and owner reports for the BXA V10 describe exactly this kind of cold roughness that is more noticeable under the light load of Drive.

Thoughts, suggestions?? Anyone? Anyone?

#2

Does it get better, when you release the brake? If it does, it might be transmission related. Can you post a video?

#3

My car does the same exact thing. I do have the tune and my manifold is gutted and my cats as well

#4

usually people get the JHM tune to try and reduce this issue. And while most of the time the JHM tune will help. The issue tends to be more mechanical. I saw this on my S6 about a year ago. It came out of nowhere from what I could tell.

The tough thing is it can be a mix of a few things. If you have bad cold starts before you do anything or put any load on the motor. Those tend to be more or less leaks. The leaks can be from the intake or the intake PCV system. That system tends to weep and leak.

The actual PCV tends to have issues when you put a load on the motor. As the spring tends to pulse.