# Odd idle/low-rev problems



## ChrisSoutham (Jul 19, 2010)

Hi, I recently purchased a lovely Audi A6 - done 127k miles with a timing belt change at 108k. Ran perfectly. 
The battery was giving me a bit of grief so after charging a couple of times, I swapped it out for a Bosch Silver. 

I'm not sure if it's related but now I'm suffering from odd idle/low-rev problems. 
Sometimes on a start (cold or warm) it starts fine and then the revs dipe to sometimes as low as 200 before bouncing back up and eventually resting at around 900-1000. 
I have had one occasion where the engine dipped so far it stalled. You can also feel the accelerator engage slightly too. When parking or travelling very slowly you need a fair amount of revs otherwise it'll stall. 

Having done a little research, some say the ECU needs resetting after a new battery is fitted, others say it's worse than that. 

Has anyone got any idea? 

Other than that it runs perfectly and strangely I don't get the same problems when in reverse! 

Yours, 
Chris


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## O_o (Nov 12, 2009)

The usual suspects are a vacuum leak, dirty throttle body/IAC, and clogged/stuck EGR valve. All of which you can repair on your own cheaply (well, an EGR valve can be a bit pricey...). There are many other things it could be though, and the fact that it doesn't stall in "R" indicates a possible transmission problem. Does it stall/surge in "N"? I know very little about the auto trans on this engine, but usually, stalling only in forward gears is an indication of a fubared torque converter, or the overdrive clutch sticking.

Also, I have a vague recollection of there being a recall on the transmission control modules for some models. I don't remember which models, what the problem was, or what the symptoms were, but it's worth looking into.


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