Cold start question

A6 All/ S6 All
#1

I’ve had a strange issue the past few weeks. No codes, vag scan is clear. Car starts cold the way it always did, everything seems normal, until i go into any forward or reverse gear, then it runs very rough, almost seems like it’s going to stall.

Put back into park/neutral, keeps running rough which i can clear with a quick tap on the pedal, but the same happens when in gear again. After about 1/2 mile of driving it goes away and hasn’t happened any time when warm.

I’ve tried going into gear as soon as it starts, different gears, forward then reverse, but always the same result.

I have JHM tune with SAI delete and it’s coded out. I’m aware of the usual rough running to get the cats warm, but didn’t know if anyone had the issue relating to transmission in drive.

Car seems to have full power, no other performance issues. I’ve checked for vac leaks, but can’t find anything.

Any thoughts?

#2

My car is also JHM tune/SAI delete and has the same behavior. Never does it when warm and mine only lasts 20/30s when cold. If I start the car it’s fine, but shifting to D or R results in rough running/lurching etc. but only for that short bit. Then it stops and everything is fine. I also have the low speed dividers removed and intake spacers.

the car has exhibited this behavior since having the tune and all the other work I had done (flow matched injectors/carbon clean/LW crank pulley, all new gaskets/oil sep, etc) My local indy shop has looked at it twice and can’t find any clear cause, chalked it up to mods and I love the performance with the tune so I have just let it be.

If I sit idle for 15/20 sec it is reduced in severity. My car has this behavior in the AM after sitting all night or after being parked 8hrs at work…

You’re not alone!

#3

I’ll chime in as well.

Have the JHM Tune, and same similar cold start stumble.

My cold start routine has been this: Start car. Let the fast idle go down to regular idle. Let car run for 30 to 60 seconds. Shut it off. Restart.

After that it seems to be fine.

#4

Thank you both for sharing your experiences. For some reason it seemed worse than usual when i posted, it’s not consistent, worse some days than others. Seems to be more of a nuisance than a problem, and a very small inconvenience considering benefits of the tune. I’ll try the shut off and restart this week and see if that helps.

Thanks again

#5

This seems to be uniform. If you don’t go into gear before the idles drop, it’s even more pronounced. I don’t have the SAI delete and this is something that was happening before I got the tune. It seems to be the engagement between the engine and transmission causing a rough idle. If I let the car warm up a bit, it resolves the problem before I ever put it into gear. When it does cause an issue, when I go into gear too early, I shut down the car and restart. That is probably always the best bet instead of trying to resolve it by pressing the throttle pedal. I know we’re not supposed to just let our cars warm up, but I guess you can clear any buildup that results by giving it a daily italian tune up.

#6

As mentioned by SIXSIX its not the JHM tune its part of the OE cat warm up schedule. When the car is too hold or the temps are too hot the car goes though a warm up cycle. It lasts about 60 seconds. Its cat related. The JHM tune makes it better but its still going to need to go though some cat warm up cycle as long as you have a cat.

Its all temp dependent.

#7

All normal, those cats were inserted into the “design” after the fact :-\

As others have pointed out In more extreme temps it’s worse especially with SAI and warm up.

I will say my 08 s6 on stock everything aside from CBE and msds filters in Washington DC exhibited less issue with this, or maybe this forum makes you think more :wink: probably because it was driven in mostly mild temperatures, aside from a handful of hotter summers. Although I doubt that’s 100% accurate since I think six is in the mid Atlantic area as well.