I have an '89 XJ, 4.0 ax-15. When its cold it runs fine, but after I drive if for half-hour or so, its performance goes down. It starts to hesitate really bad. I was told the O2 sensor might do that. Any thoughs??
Thanx Justin

definitely sounds like an O2. before you replace it check the wiring, I cut one of my wires once and it is the same as a bad O2.