Recently bought a 2000 XJ that had a blown head gasket from overheating. Basically the water pump was trashed and had never had any coolant service. I tore the head off to check internals, the typical head crack issues & just general review as this is a new project that I haven't even sent through inspection yet. Everything was good with exception of the #2 cylinder which looked like it wasn't firing but still showing compression when I later tested it. (wondering if my injector isn't working properly) After the head & coolant service I replaced the thermostat, water pump, spark plugs, coil rail, TPS and clock spring due to a OBD read out of P0121, P0122, P0123 & a tranny code I can't remember at the moment. After some research it stated that the clock spring is often the biggest issue based on my symptoms & codes. So with all that said my question is based on it's rough idle and sputter when in gear. Has anyone else had these additional symptoms? Could it be a bad O2 sensor or maybe my injector(s)? Would a fuel treatment & fresh tank of gas help - I'm not sure how long the vehicle sat but it started right up when I bought it. My cats look clean & in good condition and everything is stock otherwise. I feel as though all those services should have cleared up my initial issues & the idle problem but no dice. Any help would be appreciated.

 

I'd definitely throw some fresh gas/fuel treatment at it before going too much further. You'd be surprised what bad fuel will make a vehicle do. If that doesn't work, I'd go the clock spring route. The change out isn't too complicated and like you said, your symptoms sound like you're in the ballpark.