Idle all over the place...suggestions

[ChrisFlo]

I've recently taken my 98 gst back to stock, and have had some trouble getting the car to run well. When I start the car, the idle holds steady at approx. 1k RPM, then shoots up to 2500 or so, then falls back to 1000. It continues to do this until I turn the car off.

Fixes I've tried:
TPS
MAP sensor
Front O2 sensor
ISC
Vacuum/Boost leak test
Spark plugs/wires (new)

I also have a new MAS on the way. Does anyone have any suggestions or experience with this type of problem? Anything will help. Thanks.

Chris

 

[1gcrazy]

Were you getting any leaks out of the throttle body? MAS might work... Do 2g have issues with their ecu caps leaking?

 

[mhuffman]

I've recently taken my 98 gst back to stock, and have had some trouble getting the car to run well. When I start the car, the idle holds steady at approx. 1k RPM, then shoots up to 2500 or so, then falls back to 1000. It continues to do this until I turn the car off.

Fixes I've tried:
TPS
MAP sensor
Front O2 sensor
ISC
Vacuum/Boost leak test

I also have a new MAS on the way. Does anyone have any suggestions or experience with this type of problem? Anything will help. Thanks.

Chris

Do 2g's have a FIAV? (fast idle air valve)? If it malfunctioned, it could possibly bring ## idle up, even though it supposed to close completely after the engine reaches operating temp.

 

[ChrisFlo]

Generally 2g's will not have problems with leaking caps. As far as the FIAV, I'm honestly not sure if 2g's have them or not. Anyone know the answer to this and how to go about checking it? Any other suggestions will be appreciated. Thanks.

 

[Spooling99]

Have you tried to uplug the ISC and use only the biss screw? The ISC is actually just a stepper motor. I know it worked on my 1g not to sure about 2g's though.

 

[GloriousDSM]

Try this

http://vfaq.com/mods/BISS-1G.html

http://www.dsm.org/how-tos/tttt/tttt3.html

That might help and shows you step by step if this is the problem

 

[Tsi_User]

Do 2g's have a FIAV? (fast idle air valve)? If it malfunctioned, it could possibly bring ## idle up, even though it supposed to close completely after the engine reaches operating temp.

IF your 2g has a FIAV I would work on blocking it. I did it on my first gen and not only did it ix my idle while it was warming up but also fixed the typical high idle i was fighting.

Do you have two coolant lines running to the front side of the TB?

 

[ChrisFlo]

I does look like I have two coolant lines running to the tb. How do I block the FIAV?