I recently purchased a 2000 XJ Classic with a 4.0 and an automatic. Test drive was good, but soon after, the engine would die when the temp reached 210 degrees. Crank Position Sensor seemed to fix that, but new problems keep developing. Throttle Position Sensor, but volts check out ok. I replaced it anyway, it is still throwing the code. It is throwing Park/Neutral Switch, O2 sensor codes as well. The fuel gauge works intermittently. The cruise works if the fuel gauge is working but trying to turn on the cruise when the fuel gauge quits will kill the engine. The tachometer quits from time to time. Now the voltage is fluctuating. Computer?????

 

keep it simple start with good clean batt connectors. all i hear here is "check grounds" so check them.
others will soon ad more,better advice!!

 

as nujeep said, check your grounds and cables. Make sure the cables and terminals are good, clean, and tight. Bad grounds can cause weird stuff to happen. I think there are 2 main ground straps, and you will also want to check the battery cables, and the alternator cables, and the power distribution cables too. Once you have done that see if any issues go away. If you are getting codes, post them by number, and give a description of the problem. Having the number helps.

 

Thank you gentlemen. I will check. Here's hoping.