Runs rough at a certain pedal postion

[BAMCHEROKEE88]

My XJ (88 4.0L w/125K auto) runs rough/spudders at a certain position of the gas pedal. It`s right at cruising speed on the highway. It has been getting a little worse since I got it in Feb.. I replaced my plugs a week ago , got more power but the spudder was slightly worse than before. Yesterday I replaced my exhaust ( Dynomax muffler and new OEM style cat from Quadratec). The spudder ( for lack of a better term ) has become even more noticeable and annoying. Any ideas?

[PearlCountry]

Throttle Position Sensor (TPS). Do a search, lots of information here on the subject. While your at it, clean the throttle body real well. Do a search on that too so you don't ruin anything in the process.

[Matthew Currie]

Adding to the above, the TPS needs to be adjusted properly on this model. If you do a search you should find instructions for doing this with a voltmeter. I found with mine that it was pretty sensitive, and too high an output voltage made it spit when you hit the gas.