We all know about the infamous Jag rough idle and chase it by replacing plugs, wires, cap, rotors, looking for vacuum leaks, adjusting the valves, converting the ignition, etc. Well, mine was solved by replacing part EAC1301, the rubber sleeve that connects the 90-degree intake elbow to the throttle body. I replaced mine on a car with only 22,000 miles while I was replacing all the fuel rail to injector hoses. It was purely one of those "while I am there items" and not until I removed it did I discover that it had a crack running the entire length of the sleeve. Needless to say, unmetered air was leaking past this crack and was contributing to my rough idle. Once all back together with a new sleeve the car runs nice and smooth.

Just thought I would pass this on to those who are still fighting a rough idle and have yet to check this part. For me it was my issue.