Hi there,

That code is a programmer's simpleton misnomer. The diagnosis is an acknowledgment of a RPM issue jumping out of its perimeters. Many things can trip that "probability" number, if it repeats enough times.
Apparently yours qualified!

When you engine operates normally it should race up and back down up upon starting to an even idle. No touching the pedal, just turn the key and it starts to idle.
That's how you can tell if the IAC is working properly or at all.

As far as idling "evenly" the IAC will not do anything else, unless, its compensating for "something else" that should not be happening.

On your "year" car it has an automatic return spring built in. When this IAC quits working it will not raise the idle at all. It will be hard to start unless you give it some air with your foot.

The IAC's can get dirty or wear out but there is no set mileage of when "worn out" or "dirty" occurs.

Taking the IAC off and trying a service cleaning is helpful. All hoses and even the throttle body should get cleaned out.
I test my IAC's with a small nine volt battery and tiny jumpers leads. Less current and sparking about , plus there is the warm dry bench instead of using a big ole' battery.

I do this to check for smooth operation opening in pulsed increments. When cranking the engine the voltage falls in the system to about that much. I observe how the spring is twisting without sticking.

As in one of Glen Yarbourgh songs about a Mendocino Woman, "It's just a THING, I do!"

The IAC does not send back any signals but has to have them from the ECU. You might want to check the connector if it's not doing what I describe in the first paragraph.

If you have some air sneaking in from other "hose" or a bad intake " manifold gasket" sources behind the Air Mass Meter, then all bets are off!

A battle begins with the rough or unsteady idling that might even cause a clack noise to emit from the engine when the RPM swings too widely. The ECU mixtures and ICU ignition timing jumps around but it is always behind things trying to play catch up!

Having Zero air leaks and a properly adjusted throttle body can make a big difference in having no hesitation take offs! Once the Throttle Position Switch clicks the IAC is cut out of the picture.

The TPS has to click upon opening and closing at the first cracking of opening the throttle. It sets the idle program and changes to run program. This creates a transition "space of time" is for the computers to work to bring on power as more air flow blends in just within the flow range of the IAC.
These things work to remove hesitations.

Another thing, always evaluate the health of the ignition system first to remove misfires for a rough idle or a surge! Any misfires gets the computer system back in the game of playing catch up!

Post back if you find something interesting or not!

Phil