first let me start by saying that i did search for this, but didnt find a definite answer. when i drive my 97 a4 1.8tqm and push in the clutch to coast sometimes, more than not, my rpms start to bounce from around 1000 to 500. this is usually in a pretty rythmic patern then it will usually calm down to about 750 to 500. also i havent really noticed as much when sitting still as when im coasting to a stop with the clutch in however sometimes it does this right when i start my engine, but not for long. when i searched this it seemed like this mainly happened in chipped cars, when they were sitting still and they were saying it could either be a vacuum line, dirty throttle body, coil packs, spark plugs, coolant temp sensor, o2 sensor,etc. in all of my searches i never really found a definite answer or condition that seemed close enough to mine, my question is has anyone figured out what is really the cause of this or know what it could be for my situation, i just got the car about a month ago so i dont know what has been done recently. Thanks in advance, Nick

 

Had the same condition on my '01 A4. Cleaned the throttle body and that took care of the problem. Really easy to do. Mine was pretty dirty, so the time consuming part was the actual cleaning of it. Used some throttle body cleaner and an old t-shirt. I got a new gasket for it, don't know if this was entirely neccessary, but I didn't want to get into it and find out that I needed it, and then not be able to get one for a few days. It was only a couple of bucks so it was worth it. Hope this takes care of your issue.

 

+1 my was nastey, had it cleaned, and reset it and it works great,

 

I'll give it a try for sure, its a good place to start being that its free. thanks for the help hopefully it works. - Nick