Hard to start, no idle

Please believe me I have searched but its hard to find a thread with the same exact problem. My 99 4.0L won't start unless I apply throttle, and it will not idle at all. It runs fine when I apply throttle but as soon as I lift my foot, the engine dies.

Currently I'm leaning toward the IAC valve, but my brother had similar (but still different) problems and it was the O2 sensor, but he got a check engine light while I have nothing. I'm just hope someone can point me in the right direction?

My sons 99 XJ refused to start without giving it throttle. In the end it was simply a dirty IAC. The good thing is that it costs nothing more than some of your time and a can of throttle body cleaner to clean the IAC motor.

I like to remove the TPS and MAP sensors as well as the IAC when I clean the IAC and throttle body (I dont like getting solvents and spray cleaner inside the MAP and TPS). Be gentle with the pintle on the IAC but make sure its clean as you can get it as well as the passage where it sits in the TB. Try not to push or pull on the pintle if you can help it as its somewhat fragile. If things go horribly wrong, both oreilly and napa have IAC motors, usually in stock.

One last tip, I like to reset the PCM after I clean the IAC. Doing a PCM reset forces the PCM to re-home the IAC pintle fully, by stepping it fully closed and then step it back to the factory preset position...helpful if you feel the IAC pintle is not where its supposed to be.

IAC cleaning, TB cleaning and PCM reset procedures can be found with a forum search.

Thank you! Big help.

Just wanted to let any future viewers know that a simple cleaning did just the trick. Jeep started right up and ran perfectly.