At almost 180,000 miles on the odometer from two previous owners, I have been working on small projects one at a time to have my XJ give me another 180,000 as the third owner. When I bought this XJ, it had 172,000 miles.
http://en.wikipedia.org/wiki/MAP_sensor
UPDATE 6/13/13: I also replaced the TPS and Idle Air Control Valve as at 181,000 it started hesitating and surging. Happy to report that after replacing the above, all is good again. Check out that vid I made to see how to locate and replace the TPC and IACV.
http://www.youtube.com/watch?v=JcesHQWrr68