Problem with rough/low RPM's

[gnarlycore]

Hi there! Have had my P5 for about 4 years now and besides really bad wheel bearing issues I've never really had anything wrong with the powertrain/engine side of things until now. I am in no way a mechanic so I always have to take mine to a shop. So recently I had an oil change done and then put a new tank of gas in my car. About 10 minutes later I notice my car's RPM's were pretty all over the place between 1K-2K when I'm stopped at a light or stop sign in Drive..and soon enough my rpms dip dangerously low and I almost stall and of course my check engine light comes on. LAME. so I take it to my mechanic and he basically says I got a bad tank of gas..he didnt give me the CEL code but thats what he says it was or something to that affect. He doesn't really do anything to fix it but changes my oil and says that the problem will probably work itself out. NOPE. Here we are a month later and still with the rough idle/almost stalling in DRIVE...when I put the car in neutral or park my RPM's are at a constant 2K and the car feels fine. I should also mention that when my car is actually moving it runs fine (aside from a sluggish start most times). What could this be and how can I fix it? If it truly is watered down gas hanging out at the bottom of my gas tank how do I get that crap out of there? Also does it hurt my car to keep putting it in neutral when Im at a stop light? Thanks in advance!

 

[bndeac]

I had this problem and found a good sized hole in my intake tube (kind of split in the corrugated part). A little bit of duct tape took care of the idle problems and the CEL until I got a new one to replace it. If it was shortly after an oil change the intake tube may have gotten shifted opening up any holes even further. They seem to get pretty brittle and mine split almost in half when I was working with it.

If the intake tube is in good shape, I know a lot of people with idle problems have found that cleaning/replacing the EGR valve can make a huge difference. Check here for a how-to on cleaning that.

 

[Tommyr]

I am having the exact same problem! I installed a SRI two days ago and since then I have been having the same problem while at stop lights. I will be idling at about 800-900rpm then it will drop to like 200 and then it is like my car revs up and catches itself. I have heard that it could have something to do with my SRI install and my MAF, so this morning I check everything over and I couldn't find any air leaks. I don't think that it is a serious issue I think that it is more then an annoyance and would really like to fix this somehow! While looking over my car I noticed that my Purge Solenoid Valve seems to be cracked. What does the Purge Solenoid Valve do? Has any one else had this problem and can help us?