Inconsistent high idle - very strange - Help? - 3000GT/Stealth International Message Center

frozenevolution · 10-27-2009, 08:14 PM

Hey all, I'm not sure if this is the right sub-forum for this, so I apologize if it's the wrong one.

I have a 92 Stealth TT, and on start-up the idle is usually ~1400. If its cold out it can go as high as 1900, then drop back down to ~1400 once warmed up. It's done this since I bought the car, but I never got around to trying to fix it till now.

I was going to go do all the steps the wiki has listed for high idles and such, but there is one thing that seems to be different from most cases of people with high idles, and this perhaps the key to a quick solution.

As I said, it usually is around 1400, but sometimes stays +/- 150, which seems like the typical high idle case. Occasionally, when I start the car it will idle around 800-900 and be perfect, until I start driving (even backing up out of the driveway will put it back at the 1400 mark). Then the 3rd scenario is when I start the car, it will start at 900, then go down to 500/600 and act like its going to stall, so I give it gas to keep it alive, and if left it'll drop back to the 500/600 mark; but again once I start driving, the idle changes to ~1400.

Any suggestions of what to try first? Thanks everyone

LeigerReign · 10-27-2009, 08:21 PM

Having the same issue but mine is like 1200. Tightening the BISS screw didnt help because on occasion it would idle at around 450rpm vs 750ish. Im convinced its my IAC. Altho, im going to check a few other things first. Waiting on a pressure tester now and then im probably going to buy a brand new IAC instead of using junkyard ones.

Also, it went away when i dropped my base timing down to 3 degrees. I dont know why.....but i like my base timing at about 8 degrees and i dont run but 12psi on 93 so i set it back and put up with the idle.

Ill keep this thread updated if i fix it.

Blurr · 10-27-2009, 08:27 PM

IAC

Get some electroncs parts cleaner and a toothbrush that you don't care about anymore. then read this.

Stealth 316 - ISC Servo Motro

The section that you're looking for is toward the bottom of the document.

frozenevolution · 10-27-2009, 08:41 PM

I'm probably going to do that IAC cleaning Friday morning (hopefully sooner if I get the chance). I'll keep everyone updated on the results. Thanks

caboose · 10-27-2009, 09:05 PM

i had a similar problem with my 92 sl and it ended up being a combination of my IAC being dead and my ECU, the first gens are notorious for leaky capacitors in the ecu and ecs computers. i recommend removing your ecu and checking it to see if your capacitors are leaking, and get it rebuilt it they are, i rebuilt mine for a grand total of about 8 dollars and it was completely worth it.

frozenevolution · 10-28-2009, 12:26 AM

ECU was rebuilt by last owner in Dec 08. It shouldn't be bad, but who knows

. If the IAC fix doesn't work, I'll check the ECU then.

dbest671 · 10-28-2009, 12:48 AM

A bad IAC can mess up/fry your ECU from what I have heard. You might want to unplug your IAC until you get a replacement, your car will run rich, but you won't fry your ECU.