weird idle

my xj has been idling a little weird lately. only after i have it in 4hi it seems. but then it goes away once i start driving again. seems to sputter a little if i rev it up. any ideas?

-tune up
-sensor(s) bad
-bad gas

not enough info.

yeah sorry for the lack of info. its just weird and pretty random, but seems to act up after being in 4hi...anything from a simple local trail exploration or jeep sledding. it was fine right afterwards, but i drove down the road to the store and ran in to get milk, and came back out, started up and was idling weird and kinda stumbling on acceleration/revving. but once i started back on the road it was fine. doesnt make sense to me, so just looking for ideas of what it could be

Just a thought, does it do it when the engine has sat and cooled for a bit?
Mine did that, I could not pin it down. Tune ups, fuel system checks, emission checks, etc etc.
I found the rarely noted problem with the manifold stud bolts backing out a bit and allowing intake/exhaust leaks. Engine stumbles, bad mileage and no noticeable noises. Worth a look into.

Well with that last post I have an idea...My 2nd [farthest back] O2 sensor electrical plug is broke off, so in theory its dumping too much fuel into the engine. Maybe its just flooded out a little from going slow in 4wd? Weird because it only happened twice so far over a 2 week period.