I have a 97 4.0/auto, and lately I've been experiencing a high idle for probably about the last 2 weeks. Not all the time but defiantly most of the time the jeep will idle around 1-1.2k and cold starts occupationally will rev up to 2k and fall to around 1500 rpms, once in gear it falls right back down to and drives without an issue 99% of the time. I have noticed that a handful of times typically while still cold at low rpms when off the gas for example rolling up to a light or sitting at a light once in a great while it will start to spitter out and feels like it will die but only for a couple seconds and corrects itself and this doesn't happen while driving. today i get in the jeep and go to start it to get to work and it cranks over and sounds as if the motor made a single revolution or two and then died, i shut it off and tried to start again and it would start to go but pitter right out if i wasnt giving it gas. it would run if i got it going and gave it excess amounts of gas but really wanted to die if i wasnt on it, i kept the rpms up and limped it to work a 1/4 mile away but died in the parking lot (hindsight should have left it at home). on my 2001 when the CPS went it did the same thing it started up for a split second and then would only crank and not start, so i am leaning towards either injectors or a fuel pump seeing that it had a high idle and will start given fuel. any ideas? anyone have some experience and thinks my problem sounds more like injectors or a fuel pump or potentially something els? once running until today it would run great once in gear i put over 400 miles on it this weekend and one more thing ill add is that it could be a coincidence but i feel as if when i had a 1/4 tank or less it wouldn't idle high as often. its my daily and i do tons of fishing this time of year chasing different species all over the state so the less time down the better. thanks in advance, any info or suggestions help.

 

I have not personally experienced a high idle problem on my 4.0l. however on other vehicles I've owned/worked on that had issues idling the problem was corrected by cleaning the throttle body and and idle air control valve. If it was my jeep I would clean the idle air control valve with mass air flow sensor spray/cleaner to start.

Also clean all your grounds in the engine bay.
When I first got my 4.0l it would have trouble starting. Would sputter and die unless you feathered the gas until it ran for a couple minutes. It acted like a carbourated engine a lot of times.
I cleaned all my grounds in the engine bay and battery terminals and now it cranks faster and runs perfect after start up every time. I was surprised that cleaning the grounds made such a difference but it did.

Both of these things are nearly free and very easy. Even if they don't solve your problem they are a good preventive maintenance measure to take anyways.
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I figured it out, (should say my buddy figured it out). But for future reference incase someone is having similar issues and stumbles across this thread. It was the idle air control valve, was going into auto zone for some throttle body cleaner when I stumbled upon a buddy who had a similar issue with his wrangler, simple 10 minute fix of taking it apart and cleaning the carbon build up. I was thinking fuel pump or injectors or fuel pressure regular which all go for over a hundred, was stoked to fix the high idle and have her running great again with simple hand tools and some carb cleaner and a rag.

 

Good on ya!

Don't be too surprised if it goes bad again fairly quickly. Sometimes that cleaning is good for years, but if it's on the border of failing, sometimes the cleaning only buys you a few weeks or months.