HELP! Yet another XJ Low, Rough Idle with Misfire Issue

Well, for those 2000-2001 XJ 4.0s that are cursed with "Hot Soak" or "Heat Soak"--the cylinder 3 misfire due to excessive engine heat on the injector, TSB NUMBER: 18-031-03; GROUP: Vehicle Performance; DATE: Sep. 05, 2003--the Chrysler fix is a JOKE. The only known down and dirty for sure fix is to put in a timer on the efan that will run the efan for about FIVE minutes after engine shutdown. Period.

The second issue is the mysterious multi-cylinder misfire, TSB NUMBER: 09-003-03; GROUP: Engine; DATE: August 1, 2003 applicable to XJs 1999-2001 and relates to the failure of the exhaust valves to properly rotate. It sounds like the OP used the MCCC--but the OP didn't post if he followed the inspection procedure in the TSB to determine if that was part of his problem.

Third, there is the LOW idle. Ok, lets simplify things for an easier discussion. An engine running LEAN will idle higher than an engine running RICH. If we accept that basic premise, then what could be causing the OP's engine to run rich? Could be those NEON injectors. I know of no recommendation for NEON injectors in the XJ past 1998.

Check the following information posted by rainman: http://naxja.org/forum/showthread.php?t=1085574

This may have been covered already... but have you thought about replacing your precat? Supposedly they can get pretty clogged over the years, 13+ years for yours probably, and it get too hot and cause misfires on hot days. Had this happen to mine once or twice on hot days and replaced the precat last summer and haven't seen misfires since.

My 96 xj is currently doing the exact same thing?

Does anyone know what range the TPS should be reading when throttle is wide open?

My OBDII scanner has a live datastream feature and it reads absolute TPS 16.5% when throttle is completely untouched and maxes out at 77.4% with the throttle fully open.

Is this normal? Is it just the way the scanner is translating the signal from the sensor, it is a rather cheap bosch bluetooth scanner?

That may be a little low at WOT, but that alone would not cause the issues listed in this thread by the OP.

bensimpson1981 said:

My 96 xj is currently doing the exact same thing?

Does anyone know what range the TPS should be reading when throttle is wide open?

My OBDII scanner has a live datastream feature and it reads absolute TPS 16.5% when throttle is completely untouched and maxes out at 77.4% with the throttle fully open.

Is this normal? Is it just the way the scanner is translating the signal from the sensor, it is a rather cheap bosch bluetooth scanner?

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