I have a 2000 xj8 with about 63000 miles on it that I bought a year ago. It has been troublefree except for a restricted performance light that has been intermittent for the past 6 months, getting more persistent the past month.

It was caused by a dirty air filter. New Frams are a little over 9 bucks at rockauto.com

 

I don't have the equipment to check the codes. It's easy to check if this is the source of the problem; just unbuckle the air cleaner fasteners so that there is a little opening between the two parts of the housing and start the car. Obviously, you don't want to do this in a dust storm! I live in the Pacific NW, so clean air is in abundance.

Ihave driven it several timesand not a sign of the dreaded light, The check engine light has even reset itself, so I'm a happy motorist.

As someone whose first mechanical projects were repacing the centerbolt in the rear spring and rebuilding the carburetor on a 47 Ford Deluxe, I learned to try to diagnose and repair as simply as possible. It doesn't always work, but it doesn't cost much to try.

 

Additionally and thankfully, I had no engine roughness associated with my situation.