I have just purchased a 1990 XJ6 Sovereign with 150,000 miles on it and everything is working well, except the car has a very rough idle with what seems to be a misfire. Once the RPM's exceed 1000 everything smooths out. I drove the car back from New Jersey to Indiana at 70 MPH with no issue at all. Does anybody have any suggestions on this

Thanks

Chris

Submitted by triath5147@msn.com on Mon, 07/05/2004 - 10:02

with 150.000 miles it could be just about anything. Not that it may not be a misfire, but i doubt it is an ignition related misfire, since once you were in overdrive, espeially under light load, you would feel it missing. Rough idle, can be caused by alot, and with that many miles, I would look at the plugs for oil or coolant residue on plug, do compression tests, and also a cylinder leakage test. just to start. Once all of these things are checked and acceptable. You can start to dig deeper.