What is an IAC motor?

Can you explain it to me in very simple terms and how it affects the hot and cold idle?
BTW, the search engine can't find it for some reason...
Thanks
Boris
P.S. 99XJ...

It runs a plunger in our out that bypasses the throttle plate.
In newer models it's called the BAC Bypass Air Control stepper motor.

Most fuel injected engines close the throttle plate completely at idle, and depend for idle speed adjustment on electronic feedback, rather than the old fashioned method of using a screw to adjust how far the throttle plate is cracked open. The IAC (idle air controller) is a little electrically controlled valve inside the throttle body, which determines how much air bypasses the throttle plate when idling, thus governing idle speed. If it clots up with carbon and sticks open, it's often a contributor to fast idle problems and failure to settle back to idle when you let off the gas. Ordinarily, the engine computer sends signals to the IAC when it senses changes in idle speed, and the IAC opens or closes quite quickly and precisely to compensate, but when it sticks, it won't act fast enough, or perhaps not at all, and idle speed gets erratic.

You can take the IAC out of a 4.0 and clean it. Do not force it open and shut by hand. It is not a plain solenoid, but a stepper motor, and can be damaged by forcing. Clean it with carburetor cleaner or other such solvents, and check for wear on the pintle at the end.

Just remove it from your throttle body and take a look at it and the hole it fits in, you'll get it then. Like said above clean it if needed.

Jason

The explanations others have given has covered the subject well, but I would like to add that as the IAC motor ages due to engine heat the motor wiring builds up resistance causing the motor to react slower. On the end of the plunger there is a angular edge which is the valve disc and the mating surface inside the throttlebody is the valve seat.
You can clean both of these by removing the IAC from the throttlebody and spray both surfaces with Throttlebody Cleaner.... Using Carb Cleaner can occasionally damage the plastic parts or sensors that it comes in contact with...
My suggestion would be IF you are going to clean the IAC; then remove all the sensors from the TB and remove the TB from the instake.... This allows you a thorough cleaning of the TB.....

Charles