I've been scouring the forums and have yet to find any "this is what fixed it" posts, so here goes.
I've got a 2000 TJ with a 4.0. For quite a while now, I've experienced intermittent 2 types of idle issues... the first one that came around was a high idle (sometimes up to 3k depending on how far down the throttle was being pressed when let off to shift) This usually goes away by pulling over and letting it idle.
The second (and most frustrating issue) is the low idle issue that occurs at random - sometimes at startup, sometimes down the road when coming to a stop... it'll idle down and more often, shut down. There is also a noticeable smell of gas at startup.
Now for the interesting part - this was taking place before my previous engine blew, and currently with the "new" engine. Prior to the old engine's death, I did replace both O2 sensors (non-cali jeep). I am also getting an IAC code - as I was with the old one, too. When the engine was replaced, so was the TB and intake. So the main things that remained the same throughout are the exhaust, the PCM, and vacuum system.
Tomorrow I have an appointment at the exhaust shop to have the cat cut off of it. If that doesn't fix it, I'm not sure where to go next - any info is appreciated