Help!! High idle won't come down!!

Probable vacuum leak.

Disconnect the IAB and see if the idle speed slows down. If it doesn't, then either the IAB & TB are dirty & need cleaning or you have a vacuum leak.

If it does slow down, then you either have an electrical problem with the IAB or TPS & need to set the idle speed once they are eliminated as being the source of the problem.

Try this... Currently there is some dispute about setting it at .99 volts but anything less is probably OK. All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a Digital Voltmeter (DVM) to do the job.

The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS

Here’s a TPS tip I got from NoGo50

When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks. Set it at .97v-.99v, the closer to .99v the better.

(copied from MustangMax, Glendale AZ)

1. Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

2. When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

3. Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

Photo courtsey of Tmoss & Stang&2birds.



See http://www.veryuseful.com/mustang/tech/engine/ for moreuseful info

My car was idling high like yours, but I just recently replaced the Idle Control Motor (connected to your throttle body) and it is idling fine now. I got mine at www.50resto.com. I'm sure that you can probably get it cheaper on EBay or at Pep Boys or something.

given the EGR gasket work you did, the above replies sound real good. here is an article which outlines cleaning idle related items and resetting the idle - omit the parts which dont apply to you. but it has pics and whatnot.

http://www.muscularmustangs.com/iac.php

also if you moved the upper around (not sure exactly what all you did), check the vac hose on the front of the upper (that goes to the charcoal cannister). they are notorius for getting baked. a stockish motor should pull 15-20" hg vac at idle.

good luck.

Hey, check it out... I searched for exactly how to set the idle a little higher, and I FOUND IT! Wow... Take notes newbies. Thanks everyone.

I would suspect a vac leak..check the TADS, PCV/Grommet for any poor fit, dry rot..check the vac lines from the EGR and into the passenger fenderwell. In my case I found the vac leak JUST inside the fenderwell after at least a dozen previous checks. Often working under the hood can damage old fragile vac lines and wreak havoc on your idle.