There've been a lot of cold/warm idle posts lately, and I figured mine could use a tune-up since I was having some sticking with my butterfly, so here's a quick IAC tutorial that I came across while surfing around.

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Posted by "Charlie":
Irratic or surging 2.8 V6 idle is a common problem with these Fieros.

First be sure to cover all the basics:

- good plugs, wires, filters, compression, no vacuum leaks, properly working EGR, timing set properly, no check engine light, and so on.

Idle is controled by the IAC valve (idle air control) via the computer and is not adjustable. Proper idle for the V6 is roughly 900 RPM.

The set screw in the throttle body is for minimum air flow through the throttle plate which is often misunderstood as the idle screw. Any tweaking of the throttle stop screw will give the ECM fits. The ECM wants to be in control of the idle and is not happy when it can't control it. If the normal learn limits of the ECM are exceeded, they will be reset to nominal, causing an erratic idle.

The IAC and associated passages need to be clean to work right. Remove the IAC carefully. You can clean it (the nipple) using carb cleaner and a small brass brush or rag. At this time also clean the throttle plate. Once clean, install the IAC back in the throttle body and reconnect the IAC wires.

For the ECM to properly control idle, the throttle stop screw must be set for "minimum air". This is a process that sets the idle with the IAC fully extended. To fully extend the IAC, jumper ALDL pins A and B together (just like when you check codes) and turn the key on, but do not start the car. With the key on, not running, and in diags mode, the ECM will keep trying to fully extend the IAC. After 30 seconds or so, pull the IAC connector off the IAC *before* doing anything else. This will capture the IAC fully extended.

(The engine should be fully warm to do this.)

Now pull out the jumper in the ALDL, and start the car. Typically the "minimum air" idle speed is in the 500 RPM range. I find the car can bearly run at 550 on a perfectly tuned engine. So as long as you can get it to idle on its own between 600 & 700 your good. (as long as it's less than 900) Set the idle using the throttle stop screw. Now shut the engine off and reconnect the IAC wires. The ECM does not know where the IAC present position is, so pull the ECM fuse (or disconnect the battery) for 20-30 seconds. (This will cause a complete ECM reset of all learned parameters, including the learned IAC ones. Then reinstall the ECM fuse.

Turn the key on, wait 10 seconds or so, and turn the key back off. This will now reset the IAC to a known key-off "park" position. Now start the car.

The engine should idle properly under control of the ECM. There are some learned values, such as an IAC offset for A/C, etc that need to be learned, but this will happen under normal driving conditions. I suggest driving the car right away under all conditions. Stop & go, steady cruising over 45 mph, full throttle, and so on. Pull over a few times and turn the car off, then restart it. The IAC can only learn X amount of counts with each run position. If everything else on the engine is in good condition and operating properly it should be around 900 RPM after coming to a complete stop with slight variations and improve over time.
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Hope this helps

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LIFE IS MADE OF OBSTACLES AND CHALLENGES — TO OVERCOME THEM IS TO PROGRESS.

DRIFTING -- IT'S NOT THE FASTEST WAY AROUND A CORNER, BUT I'LL BE DAMNED IF IT'S NOT THE MOST EXCITING.

Unless I'm mistaken, all this work can be circumvented simply by starting your car and driving it up to highway speeds, which lets the ECM reset the IAC position itsself.

Jax184, What he`s saying is --to do the proceedure if your idle set screw has been tampered with and you need to re-set the idle again--which I fooled with for more time than I care to admit--so finally got a newer t.b. with the cap still installed & all is well.

After going through the procedure, the author might not have had the "perfectly tuned engines" he thought he had. Mine's out there idling at 300 without missing a beat. Go fig.

quote Originally posted by Delphince: After going through the procedure, the author might not have had the "perfectly tuned engines" he thought he had. Mine's out there idling at 300 without missing a beat. Go fig.

Hi, Been there to many times---do have winaldl ? Its usually the fastest way to nail this down, kinda takes the guess work out of it .

I bought an 88 GT that had had the idle stop tampered with. What I finally did to fix it was to back the "idle-adjustment" screw out far enough so that the throttle plate was not touching it. That resulted in the throttle plate sticking in the bore. To correct that, I advanced the "idle-adjustment" screw until it just kept the throttle plate from contacting the bore. After that, it worked fine.

Hi, Pretty cool. Another way is to find a good one that still has the cap ( I had to do this) and measure from the bottom of the plate to the outer edge --its exactly 1 & 1/8 th inch--just like the factory set them.