This should be done as part of the major tuneup. A dirty IAC system can cause stalling when you come to a stop, or a rough/hunting idle.

Description/Operation of IAC system: Ignoring supporting systems (such as the computer), the Idle Air Control system is made up of two parts- the IAC motor, and the IAC passageway. The IAC motor has a pintle on the end, which fits into the IAC passageway. When your foot is off the gas, the computer "knows", and puts the IAC motor into action. The IAC system allows air to bypass the throttle plate, in order to keep air going into your engine so it doesn't stall. When you operate the gas pedal, the computer tells the IAC to close; otherwise, you'd be getting extra air into the engine.

The IAC passageway can be seen if you remove the hose going to the throttle body. Look to the passenger-side of the throttle body opening; you'll see a small hole. Find the IAC motor, which is on the upper-passenger-side of your throttle body. On 85-89, the IAC exits the rear of the throttle body, and screws in like a spark plug. On 90-92, the IAC exits the side of the throttle body, and is held in with two screws. Both models use a 4-pin connector on the wiring harness. If you remove the IAC motor and look inside it's hole, you'll see another small hole- that's the other end of the IAC passageway.

Cleaning Procedure:

1. Buy a can of "Throttle Body and Intake Cleaner for fuel injected engines." Try not to use carb/choke cleaner.

2. Engine off. Throw the keys far away from you. DO NOT put your keys in AT ALL until you're done with this procedure! (No permanent damage occurs, but the procedure is easier to write because I don't have to type up how to fix anything extra.)

3. Disconnect the IAC motor's electrical connector. Remove the IAC from the throttle body. Keep note of how tight it's in, if it's an 85-89 2.8. You'll put it back in with approximately the same tightness. Remember that the IAC motor is STEEL, and the throttle body is ALUMINUM. Overtighten that puppy and youll ruin the threads in the aluminum throttle body. Same with the 90-92 3.1; don't overtighten those metal screws! Try to keep the gasket intact; it'll probably stay on the throttle body. If it tears, you can re-cut one from thin black gasket material, you can buy a roll of it for $2 from an auto parts store.

4. Hold the IAC motor so the pintle at the end of the shaft points DOWN. Spray the pintle with the cleaner, and hold the motor, pintle down, until the cleaner evaporates. Do not let the cleaner get into the motor!! You can destroy the motor's windings, and you'll wind up dropping $45 for a new motor. If you hold the pintle facing the ground, this can't happen.

5. Remove the throttle body hose. Spray cleaner into the IAC passageway hole from the IAC motor's hole. (This way you're spraying from the top of the passageway, so gravity helps you.) You'll see dirty carbon run out of the iac passageway at the front of the throttle body. Keep spraying until the "stream" of cleaner is carbon free.

6. Spray some cleaner into the IAC passageway from the front of the throttle body; kind of like a back-flush.

7. Spray a bit more from the top of the IAC passageway to flush out anything that #6 pushed inside.

8. Reassemble the IAC motor to the throttle body. You can re-use the gasket, as mentioned in step #2. Don't overtighten the IAC motor (85-89) or the IAC motor's screws (90-92).

9. Reconnect the electrical connector.

10. Retrieve your keys from the shrubs into which you threw them.

11. Reconnect the throttle body hose. You're done!

 

Couple things here...

1) You can use carb cleaner, if that's all you've got - just do not hit any rubber with it!

2) My stock ('88) IAC was plastic. I destroyed it quite quickly, actually. The GP Sorenson replacement was $25 at Discount Auto, and made of metal! Do be careful, as it only has to be tightened to like 10ft-lbs of torque. That is SNUG, not tight!

3) Do not do #2 of this writeup in a cow pasture. You will not find your keys! (I've got my ignition cylinder out, to make a new set of keys. Don't ask how I know!)

4) You may notice the car idles higher now. Take her out, run along around 40 mph, then let her idle about 5 minutes. The car should re-learn your idle within that time. Mine did.

 

This should be a tech article with how often it's asked about...

My idle was higher and my car sputtered/missed just a little bit for about 5 mins because I used so much cleaner and was in a hurry that the car inhaled the excess fumes when I started it. It was carb cleaner too.... Yes, I did clean, dry off, and remove the excess as thoroughly as possible! This was before school in my friend's driveway, mind you.

 

Excellent article Tom. Like I said before I enjoy reading what you have to say. I am sure you could teach a retarded deaf monkey how to fix cars. Its not the knowledge of the subject, its being able to convey the knowledge to others so they can understand too.