2g Idle problem- VETERAN'S help needed

[ktmryan53]

Ok so i am having an idle issue on a BONE STOCK 98 gst auto. It idles to 1500-2000 rpm without load (ie "P"ark and "N"eutral). So i figure replace ISC. I replace that and no change and also replace TPS with no change. With load (ie "D"rive or "R"everse) it drops to haunts from 1200-1500ish. I pull the MAS plug and the idles is perfect at just under 1K but the car goes into rich mode and bogs when you give it gas as it should. What the hell am i missing here, i have had this issue before on another car but the ISC fixed it right away. i do need to do a boost leak test but i dont think that is suspect. Any help would be great. Also there is nothing crazy like ported throttle body,aftermarket bov,ect or other mod associated things which would casue this since they are not on the car.

 

[tenn-gsx]

A boost leak could cause this. Check your biss. Did you calibrate your tps? Is your fiav functioning properly? Did you check your readings on the ISC? Are they within spec?

 

[Boma]

A boost leak could cause this. Check your biss. Did you calibrate your tps? Is your fiav functioning properly? Did you check your readings on the ISC? Are they within spec?

+1 on tenn-gsx, he beat me to it. Also, do you have any issues when car is cold/warm operating temperatures? Do you experience sudden stuttering when car is under load or when you punch the throttle?

 

[ktmryan53]

checked isc and it was within spec. didnt calibrate the tps but when it is all the way down the car goes from 1200-1700 up and down continuously in park and neutral. i believe when it was cold it idles just above 1k in park. I also disconnected the battery and think i remember these cars being fuzzy logic ecu. Last time i messed with a dsm was 5 years ago. how do you calibrate the tps with the feeler gauge?

 

[m_0ney_pit]

basically things that cause high idle

leaky intake manifold gasket
leaky throttlebody gasket
leaky injector to manifold seals
fiav seal
throttlebody shaft seals
bad fiav
throttlebody plate
leaky biss
other boost leaks in the vacuum lines

 

[ktmryan53]

i think the only possible options would be-
fiav seal
bad fiav
leaky biss
other boost leaks in the vacuum lines

I have the BISS screwed all the way in which should be letting the least about of air past. I also check the o ring on it and it is fine.

 

[luv2rallye]

Also make sure the Idle Position switch (on the TPS) is adjusted correctly so the ECU knows it's at idle: http://www.dsmtuners.com/forums/newbie-forum/79304-tps-test-readings-need-help.html#post660531

 

[ktmryan53]

Ok quick update- started the car this moring and it idled perfect for about 2 min until the temp gauge began to move up which then the idle began to also increase.

solved.

 

[tenn-gsx]

So what solved it?

 

[bertrenolds]

It was probably a vacuum leak.

 

[tenn-gsx]

Probably is cool. But the OP should put up his findings so that others can use his experience to help them if they have the same issue.