Bought a used 1998 XJ. 4.0 I6. Sat for a year with very little fuel before I bought it. Put $10 of gas in it and it ran great for the first 75kms. After putting in half a tank of gas and driving another 15kms up the hwy, it started to sputter and bog down between 2k and 3k rpm.
Parked it and swore at it for 10 mins, fired it up and drove fine for a while but returned quickly. Drove for the rest of the night and the problem improved. Friend of mine drove it hard around the block without any issue. As soon as I drove it right after it began to do it again, but not as bad.
Idels great. Even if I rev to 2000 to 3000 rpm while parked it doesnt do it. Just when Im accellerating.
Long winded I know, just wanted to share the while experience. Im thinking maybe some water in the fuel or fuel filter/pump. Maybe just needs to be ran? Any ideas would be appreciated. Thanks!

 

Sounds like a fuel pump issue, there is not a serviceable fuel filter on a 98 XJ. There could have been water in the tank too, condinsation will build in the tank if it is left setting for long periods very little fuel. It might clear up after you run a tank of gas through it, but the pump might totally fail too. Who knows? FYI, fuel pumps usually fail right after you get done topping off the tank, just ask Murphy.