What is the idle air on a Jeep Grand Cherokee?

Answer 1

The Idle Air Control (IAC for short) Motor controls the idle speed of the engine. There is a little pintle that moves to open the throttle just enough to keep the Jeep's engine at proper operating idle speed. Sometimes the pintle becomes carboned over or damaged by hyperextending itself.

Symptoms:

A low "Cold" idle speed. Normal "Cold" idle speed is 700 - 1000 RPM. 700 RPM is just below the second line above the zero on the tachometer. My ZJ would idle at around 600-650 on cold starts.

Sudden drop in RPM after cold start up. In the morning or after my ZJ sits for a long period of time, I will start it up and it seems fine but when I pull out of my driveway, turn the curve at the end of the cul-de-sac and hit the brake for the stop sign, my ZJ's RPM drops to 250 for about one second, then jumps right back up to the low "cold" idle speed.

Low idle. Yes, the most common symptom is low idle. I will be sitting at a stop light in drive and the ZJ's interior is just vibrating. It's a free back massage! It may seem cool but it's not good for our engines. My ZJ would idle at around 500 rpm hot.

In terms of replacement of the IAC motor, it's very easy but not very cheap. In this case, I will highly recommend a Mopar brand IAC Motor. They rarely go bad. My old ZJ had 140K miles and it idled perfect. It all depends on how much you service the throttle body. The more maintenance you do on it, the more likely the IAC will last since it will have less carbon on it, preventing it from seizing and ending up like mine. Some people has sprayed enough throttle body cleaner into the hole on the throttle body where the IAC is and have fixed it but I think it is easier (yet more expensive) to replace it.

If you think you need a new IAC Motor, I would try a tune up first because that may be the problem with the engine. When I say tune up, I mean:

New spark plugs, spark plug wires, distributor cap, rotor, fuel filter and air filter. Also, clean out your injectors. Running one bottle of Redline Complete Fuel System Cleaner will clean out your fuel system. Don't forget to clean out your throttle body!

Tools required:

1 Torx head socket or screw driver

Removal:

1. Disconnect the battery

2. Take off the air cleaner tube

3. Locate IAC Motor

4. Unplug the IAC Motor harness

5. Remove bottom screw

6. Remove top screw

7. Slowly remove IAC Motor

Now, at this point, you can compare the new IAC Motor to the old one. My old one was hyperextended and carboned over.

Installation:

1. Put new gasket on IAC Motor's shaft

2. Place IAC Motor back into hole

3. Using the new Teflon-threaded screw, install the top one first, followed by the bottom

4. Reconnect air cleaner tube

5. Reconnect battery

6. Turn the key to on don't start the Jeep. Let it sit there for 10 seconds.

7. Start your Jeep and let it run for 3-5 min. The idle will start high (1500 RPM) and will end at the correct speed. After the idle speed has settled. Turn the ZJ off, and then start it again.

8. Congrats! You've fixed your idle speed problem. If this didn't fix the problem, the next step in the line of replacement is the throttle position sensor.

Quoted from:Jeepsunlimited Forums