Just as a follow up for people with the same problem. I sold the xj because it was a engine problem. When my mechanic did the leak down test it was not having the idle issue. I bought my own gauge and waited for the problem to arise. I performed a compression and leak down. Compression was less then 100 and air leaked out into the valve cover. Seems after talking to a master tech at my local jeep dealer that the 2000-2001 xj had a known issue of the exhaust and intake valves not rotating. This causes them to wear funny and only seat right in one position. This caused my intermittent problem. When I high reved the engine it would cause them to rotate and not seat correctly for a while. Hope this helps others with the same issue.