Ok first off, help me out here on understanding fully about what the IAC does. I know it aids in the idle, but what else? I don't really think mine is working? When i unplug it when my jeep is running nothing happens..... when i turn on my A/C the idle goes from 800 to around 500, so is the IAC supposed to bump the idle back up? When i start my jeep it goes up to 2K rpms and then gradually back down, but after 10 secs of running the idle becomes really "bumpy" if that makes sense.... i have newish injectors, didn't help... so wondering if this will fix anything if i replace it? Thanks

 

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I have searched... hence the reason i am posting now

 

From what I know, the IAC motor is working all the time when the motor is running, and it lets the motor fine tune the amount of incoming air. On an '89 your TPS is adjustable, so I'd start there. Also check your connectors at the TPS and the IAC motor.

Already searched?

Google "how does a XJ IAC motor work?"

Google "XJ TPS problems"

Answers are right there, few thousand actually.

 

They need to make that search funtion more user freindly

 

Yes i completely agree.. i'm sure there are tons of threads on this matter, but everytime i try to search i never come up with anything..... Anyways ive adjusted the TPS, and my whole engine is brand new, along with the TPS and a few other sensors.... just still the weird idle problem, so it just makes me think that maybe the IAC would have something to do with it?

 

The IAC has a pintle that it advances or retracts allowing the ECU to control the opening around the butterfly in your throttle body. An advanced IAC will allow more in, a retracted one will allow less. It should advance slightly (powered by a relay) when the ignition is turned to off; this is to prepare the engine for the next startup (the equivalent of giving it some throttle to start on a carbed engine). When the engine starts, the ECU should retract it slightly until the idle reaches the correct speed and the oxy sensor detects the right mixture of air and fuel. The ECU uses your Oxygen Sensor and MAP sensor to determine the exact space for air to flow around the butterfly, and will make very slight (hard to see) adjustments accordingly. I'd start with your oxygen sensor, test it with an ohmmeter. If you unplug your MAP sensor with it running and it dies, your MAP sensor is probably fine.

Edit: When I say unplug your MAP sensor, just pull the vac line, not the electrical plug. One other thing, check all your grounds, including the one for your TPS and MAP sensor. If those show any resistance to the ground/negative terminal of your battery, re-wire them to a reliable ground (like where the engine is grounded to the firewall).