Car wont idle at a constant RPM + CEL

[2TSiAWDs]

I just bought my second DSM. I love my first one. Last year I bought 1990 TSi AWD with 8000 original miles. No not a typo just VERY lucky. I love it to death and have since bought a 1995 TSi AWD because of the way my other car has treated me. Plus I always liked the 2G body style. I am trying to smog the car however the idle is sporadic when the car is in neutral or park. It is an automatic. The revs go from about 1500 rpms to about 1900 rpms and it drops back down. A whole cycle takes about 1 second and repeats over and over. Occasionally it will sit and idle at about 1600 rpms and stay there. In gear the idle speed is about 950 however it feels as if it is applying throttle even at idle speed. The other problem is the check engine light. It has worse than a mind of its own. This morning before I started the car it came on and then wouldn't go off until I reset the battery. Later after a hour commute and no problems, I took it for a short drive and then it started with the idle problem. After letting it set at idle for 5 minutes I still had no CEL. I shut it off and drove it back to work and never thought about it again. Until after work , I drove it home , a 2 minute drive, And it was not giving me the idle problem however when I pulled up it threw me the CEL. I have no clue what to do or where to start as I am a total noob to the DSM community. I am not stupid as I already tuned up the car and checked all of the connections and hoses. However like I said I don't know much about these cars of how to fix their problems. Any help would be greatly appreciated as I am trying very hard to get it running right and smogged.

 

[-LA-]

Have you checked and seen what CEL your getting, first?

Then there is alot of threads on idle surge on this site. Just search for it.

It could be alot of things. Mostly sensors and stuff. Get the CEL so you can see what is causing that first.

 

[turboboy4]

Just get yourself a cheap scanner from like Checker or something, and run the codes to see what the cause of the MIL light is, the problem could be related but check codes to make sure.

 

[2TSiAWDs]

Thanks for the help. Belive it or not it was the idle adjustment screw on the TB. I turned it in a little bit and now it idles right under 1000 RPMS. I had a friend run the scan code and my temp sensor for the ECU is not working or the wiring has fallen apart as the code is it will not go into closed loop operation for the coolant system. That makes it run rich all the time as it thinks the car is cold and that is what failed my emission test. Thanks again for the advice.

 

[-LA-]

coolness. Glad to see you got it. Good work.