The other day, I start my car and it was idleing very low.. around 500 rpms even when I started the car in the morning. It wouldn't go to high idle (1100rpms) and warm up like did previously. Now when I start the car, it idles really high at around 1700-1900 and it won't go down. I've reset the computer with no help, reset the idle screw and that seemed to help for all of 5 seconds. I disconnected my Crane HI-6 and used the stock coil and that didn't help. Checked the cruise control cable, no binding.. The throttle body linkages is free, there isn't anything pulling on it. I checked for codes and there aren't any there either. Recently, I've put on SLP runners and ported the plenum and a Kenny Brown STB (like that's gonna cause a high idle but I thought I'd mention it) I checked the plenum bolts and they seem to be pretty tight so and since the idle is constant, not surging, I don't imagine it'd be a vacuum problem. If anyone's got any ideas, I'm open to suggestion and for things to check.. Thanks.

-Bruce
89 Firebird T/A 305 TPI Auto
Edelbrock TES, SLP Runners w/ ported plenum, March Underdrive Crank Pulley, Accel Supercoil, Crane HI-6, Energy Suspension Engine and tranny mounts, Flowmaster Muffler, Jet Airfoil, 170 stat, !MAF screens

 

Bruce,
It sounds to me like the IAC (idle air control) solenoid is on the fritz. I would guess that initially it wasn't opening enough to allow for a decent idle. After you drove it for a while(or next time you started it) it may have opened up and stuck in that position. Now that it is open too far it creates a fast idle because of more air getting by it(pintle).

I am not sure if it would throw a code or not if it's defective. I don't think so.

There is a method for setting the pintle position(if the IAC is not damaged)....something like 28mm overall lenght. I will check on this and post again.

Other possibility.....vacuum leak that you can't find. They can be very hard to detect.

Just my $.02 worth

Mike

 

So I checked my IAC and it was kinda dirty so I cleaned it and pulled the pintle out and cleaned that, cleaned the spring and the piece on the throttle body so it was clean too.. I made sure it extended and retracted and it works fine.. but I still got problems.. I checked the motor, it works when it's plugged in but I also checked the resistances in the coils.. It looks like I might have lost one of the coils in the IAC. I'm getting something like 56 ohms over one and open on the other.. If someone knows what I'm supposed to be reading (I'm assuming two resistances over the two sets of contacts), I'd appreciate it.. If not, if someone's got an IAC that works, shoot me an email. Thanks.

-Bruce