My catalytic converter was rattling, so while I had it in the shop I had the mechanic install a new one. Now my 98 xj is missing badly. Since the only other thing he was doing involved my steering, I am assuming the new converter is the culprit. I may be assuming wrongly, so I am here to ask if anyone has had some similar problem?

 

Dont know. Its possible they damaged the o2 sensor wiring in some way and the PCM cant get a good reading off it. Crawl under it and make sure its plugged in good and the wiring isnt damaged. Its not much, but its a start.

 

The rear o2 sensor on your 98 is really only to check if the cat is working, the upstream O2 sensor is what handles fuel map and tuning related stuff.

no codes are being thrown? Off the cuff it sounds like a CPS or TPS issue but that is just a shot in the dark.