NatesL98

I have a 90 iroc 5.7 TPI with some basic mods. headers and no cats, msd coil and wires but other wise bone stock. after a day of driving i got back in my car and it would not stay running. the idle was low. i turned the idle up to keep it running and it did fine for a while. now sometimes you can start off driving and it will run fine. if you get out and it cools slightly (i am only assuming it cools) when you start it up the idle is around 2000rpm sometimes as high as 3000rpm. sometimes it will come down while driving and some times not. when the idle is high it uses an extreme amount of gas. I have replaced the IAC and the TPS. please help. i read the tech article on IAC adjustment but am not sure if I did it right. I have searched threads all over this sight but cant find one with the same prob. PLease help

1fastam

iTrader: (1)

did you clean the iac passage before installing the new iac, if not it could be sticking causing it to idle high. if the iac doesnt close when it needs to its like having a vacuum leak,ie: high idle. also check for vacuum leaks.hope this helps,later jimmy

NatesL98

I took the TB off and completly cleaned it. if it was a vacuum leak wouldnt it be a high idle all the time?

zrated57

At first I'd say the IAC may be defective, but you've replaced it and the problem wasn't cured. I wonder if a bad MAF sensor could cause this?

NatesL98

I have speed density not mass air flow, could a sticking EGR cause this? I am trying to eliminate all possibilities before I suspect the ECM.

1fastam

iTrader: (1)

you said you idled it up in your first post, have you idled it down since replacing iac.if the egr is stuck open it will cause low, rough idle.you can take a 2 foot long piece of metal stick it against the egr and tap on it with a hammer to loosen the carbon buildup.look in the tech articles on homepage, look for setting iac and tps adjustment.later jimmy