Re: 2001 WJ Misfire
Welcome to the garage.
The TPS seems to have a problem. I would reset the codes and see if they come back. If so, for P0121, i would start changing the TPS.
If you still have misfire codes thereafter, i would check the fuel trim figures with a scanner, to see if the PCM maybe is down trimming the fuel injection pulse to a level that it will cause misfires (too lean mixture will not burn well).
Do you have the I6 engine?
If you donīt have a scanner, but do have an android phone, you could buy a cheap bluetooth dongle and download the free app Torque.