Rough idle and hesitation?

I recentley got my first jeep a few weeks ago and yesterday I took my kids to school in the morning and everything ran perfect, go to pick them up in the afternoon and while waiting for them to come out it started to idle rough. While driving home it had a hesitation when accelerating. Well to complicate things I went out to drive it around last night to see what was wrong and it was fine again, I also drove it around tonite and its still fine!! It recently had a full tune up done and the air filter cleaned and oiled (k&n intake). Any ideas on what could have caused this? I have gone over the typical stuff and everything seems fine, I did notice in Chiltons it said to check timing, its a 94 4.0 with the K&N intake and Magnaflo exhaust from the cat back. Would the timing be done by the computer or still with the dizzy? Thanks and please pardon my lack of knowledge with this motor, I went threw Chiltons and just curious if this is a known issue thats simple to fix or just a fluke? I had this posted in the Street and Performance and was recomended to move it here so please excuss the double post, Thanks

1. Start a fire.

2. Burn the Chiltons.

Timing on a 4.0 is controlled by the PCM based on input from the crank sensor, and is not adjustable.

Any number of things could cause the problem in your 94--ignition, fuel, the synch sensor in the distributor (for input to the PCM on firing the injectors), the injectors, the sensors.

You may have to wait until it is in a bad mood again to try and find the problem.

I recommend you buy a FSM for your year, you can get licensed CD or reprint versions here: http://www.autobooksbishko.com/index.html

Stay away from Haynes and Chiltons, too generic, cover too many years, and too many errors.

As mentioned, the FSM is a better resource. Chiltons and Haynes are pretty generic and cover many years, the FSM is specific to your year XJ.

Intermittent problems are tough to find. If it happens once, I don't get too concerned.

If it returns, time to start chasing it using a methodical simple-to-more complex strategy.

A bottle of high quality fuel injector cleaner like Lucas/Techron/BG44K, etc in about 3/4 of a tank of gas is never a bad idea.

When you mention "full tuneup", that should include spark plugs, plug wires, distributor cap, rotor, and fuel filter.

I was told a full tune up but last night I was replacing my rear oil seal in the tc and the fuel filter was not changed so that might have something to do with it !

i would pull the iac valve out and clean it. 2 t-25 screws on the throttle body and some seafoam do it nicely. lots of gunk in there thatll screw your idle up. just dont push on the plunger or youll be buying another one. just carefully wipe it with a q-tip. then put the rest of the can threw the intake as per the instructions. seafoam is a wonder in a can for 7 bucks