Let's see if any of you guys have experienced this before and can lend a hand.

A friend just brought over his 89 IROC with the 5.7 TPI. It appears to be stock except for the exhaust. He's having a problem with it stalling on him when he comes to a stop or changes from drive to reverse or park. I took it for a ride and what's happening is when you take your foot off the gas it still idles around 1200 and you can feel the engine pushing the car still. When you use the brakes to come to a stop it either dies immediately or idles high and then the idle drops until it dies.

I hooked DIACOM up to it but could only check it at idle as my laptop battery is toast. TPS voltage lookes fine as did MAF readings. Also it went into closed loop and was switching between rich and lean. In Park at idle it was running about 50-100 rpm's higher than desired. The weird thing I noticed though was that at initial startup the IAC counts went into the 100 range for a few seconds, dropped to about the 20's and 30's for a few more, then they zeroed out. Now I'm no expert but shouldn't I have atleast a few IAC counts at idle? If not then the IAC is full closed and the engine is getting too much air right? This is what makes me think that the min air setting is off. Am I off base here or in the right area? Could a vac leak cause these same symptoms as well but maintain a steady idle in Park?

 

First thing I would do would be look up the TPS/IAC setting procedure here and follow it.

Then see if it persists.

If it does I would start checking for vacuum leak or a possible bad IAC or gummed up IAC/throttle body.

Look at the TB and make sure blades arent hanging up on carbon either so when u "set" it its actually being held up etc.
later
Jeremy

 

I concur. It seems that someone has been toying with the throttle stop screw, or there is a vacuum leak somewhere. There should be some IAC activity even at warm idle, else the ECM is not truly in control of the idle.

 

Thanks Vader...just wanted to confirm my thought process. I'll try resetting the minimum idle as per the tech article and report back.

 

I reset the min air and the IAC counts came up slightly but the car won't stay running still. No more high idle on decel I don't think but when I come to a stop it will idle ok for a few seconds and then just die. Could this point directly to a bad IAC motor that's not moving fast enough?

Also I haven't done one in a long time...do I have to remove the TB and take the bottom section off to get the IAC out or can I do it in car by just unscrewing it?

 

Pulled the IAC out and it was clean as a whistle and so were the passages and throttle blades. I'm a little stumped.....my best guess is an EGR problem? I went around with brakleen and didn't find any obvious vac leaks at the intake.

I bandaided the problem for now by turning the idle up to about 1200 in park....in gear with your foot on the brake it's around 1000 which is high but will keep the car running for now.

What do you guys think?

 

just a thought and because you stated it does it when you stop which means you're appling the brakes, might consider looking into a possible vacumn leak at the brake booster, just a thought of something out of the ordinary

 

It was clean? Even the rack? It only takes a little varnish on the rack to make the IAC very sluggish. I always like to clean them, apply a little oil, and retension the spring a bit.

 

Thanks for the diagram Vader.....I actually pulled it apart and cleaned it when I had it out anyway and it was of no help. He's most likely got a vac leak that I couldn't find or an EGR problem. I told him to have the dealer diagnose it since I don't have the pump for testing the EGR valve. Too many other projects going on right now to chase my tail on this car.

 

Well i had the same problem in my 1987 tpi, accually only a few days ago, i took my throttle body into shop cleaned it to F*** hell and replaced all the gaskets, hen threw it back on, and reset the iac


Made the biggest differance ever lol

 

SOinds similer to an idle problem I am having. It just surges up and down. New IAC, checked for vacume leaks as well. No luck, you can watch the AF go real lean when the RPM drops.


I am stumped.

 

myn kinda jumps up and down 100 rpm, till its about 130 degrees and up, i hear it could be a bad egr valve but it isnt hurtng it so i dont care lol

 

Did you remember to disconnect the timing bypass connector when you adjusted the idle speed, I don't think the tech article says anything about that.

Also after resetting the idle speed you may need to readjust the tps. Depending on how far off the idle speed was, the tps could be really off.

 

Disconnect the timing for Idle sensor? Never heard that before, guess I'll do it again.