Idle Problem

[RT-AWD]

I bought my 91 TSi AWD about 8 months ago and recently its been idling very strange. When i start the car it goes to 1500 rpm and settles at 1200. Then ill drive it normally (no high accel or anything) and ill stop at a stop sign and the idle will be at 700, and its more difficult to launch. Then after the car has been running for awhile it'll start idling at 2200.
I tried another IAC motor i got off a friend but that didnt help. I'm not sure my friends motor was any good. What should i do?

 

[Glliw]

I would first start with a boost leak. Especially near the throttle body. I leaky BISS or PCV or TB gaskets could be the culprit. Check all the hoses in that area.

 

[RT-AWD]

I'm very new to this whole thing so i dont know what a BISS is. My friends newer IAC motor has so far kept the idle above 1000, but at times it idles at 2200. I'll check those gaskets thanks!

 

[Glliw]

The BISS is the base idle set screw. It is the screw in the throttle body to adjust the idle. There is a certain procedure to setting it. On that screw, there is an o-ring. Over time it gets hard and brittle and will start to leak. If you do a boost leak test, I'll bet you it will leak out of there. Spray the area with soapy water and watch for bubbles.

On all 3 of my 100k+ mile motors the BISS has leaked.

 

[RT-AWD]

Ok I will try that! Also I have a decent exhaust leak where the turbo meets the exhaust, I havent fixed it yet because I am planning on buying an exhaust soon and plan on replacing it then could that effect idle?

thanks

 

[Glliw]

No, a post-turbo exhaust leak will not effect idle. Unless its before the 02 sensor, then it might be a problem. It will effect alot else though. Your releasing those hot gasses into your engine bay, possibly melting wires and destroying electronics such as fans. Get that leak fixed asap. A gasket is cheap enough insurance against a wiring hellhole.

 

[RT-AWD]

Took car to JNZ tuning today turns out my throttle cable was stuck, but guess what.... NEW PROBLEM!! On the way home i noticed a oil smell checked oil pressure it was low, accelerated it went up, idle now surges. Is this the oil pump gone bad? I saw no white smoke at all no oil leak either.