IAC = 666.

[Rerun]

Having idle issues and a sluggish second gear, and the infamous 20 year wait for RPM's to drop when you come to an idle.

Got tired of it, I just unplugged the IAC and car runs better than ever. So, **** it, I'm running without it.

I guess I could try getting another IAC from somewhere other than Autozone and see how it does. For now, **** the IAC.

 

[HISSIN50]

hey bud. lots of folks have done just what you did. about the only thing you lose is fast idle (i think) on start up and load compensation for a/c etc. if you dial the idle up a little, it can overcome it.

not that this helps you any, as im sure you knew it all already, but just general info.

let us know how you like it in the long term.

 

[timewarped1972]

this is a good opportunity to ask questions about this little 79 dollar part.
i noticed on evil bay there are people selling ( performance chips or modules ) as they call them that plug into the iac plug or plug in between the iac and the plug. apparently verying the resistance has some type of effect can anyone answer exactly what???
for example, we know there's a piston type valve in it and i assume the position of that effects that selenoid looking thing sending a signal to the computer ( i assume it's this way, not the other way around, other way around being that the computer controlls the selenoid wich controlls the valve itself ), ok, so assuming thats how it works ( the first way ) what exactly does it tell the computer to do? does it effect timing at all? or just fuel richness or what?? will the computer have to re learn or re adjust if it's left disconnected? are their any negative effects of it being disconnected or does that just depend on the car ( some may run better some may run worse with it disconected ) ?? and what all does this thing controll??? is it just the high idle at start and ac compensation like mentioned above or is it more?? have i asked enough questions yet?? can i speak to the ford tech who desighned it? lol...

 

[jrichker]

The IAC (or IAB) is an actuator that bypasses air around the throttle to regulate idle speed under computer control. It is spring loaded to the closed position, so under computer command, it opens the little shuttle valve to allow air to bypass the throttle butterfly. More air increases idle speed, less air slows it down.

The IAC is powered from the same circuit as the injectors and has 12 volts on the Red wire going to it anytime the ignition switch is in the run position. The computer provides a ground path to the IAC to complete the circuit. The computer turns the ground on and off many times a second to control the airflow through the IAC. If you connected an oscilloscope to the White/Lt Blue wire on the IAC, you would see a square wave that varied in width and switched on and off between 12 volts and a little less than 1
volt.

In closed loop, the computer uses signals from the MAF, PIP, ACT, ECT, BARO and O2 sensors to calculate idle RPM and air/fuel ratio. A malfunction from any one of them could cause idle problems and the surging idle common to many Mustangs.

Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by James Probst :ISBN 0-8376-0301-3.

It's about $20 from Borders.com see http://www.amazon.com/ . Select boo...ope this helps answer some of your questions.