1989 Jaguar XJS idle

Hi,

I had the exact same problem on my 1992 xjs 12 cyl. At startup, the rpm would surge up and down for 5-8 minutes then it would stabilize once warmed up. When I opened the hood, it was like that engine was alive! Anyway, it was the auxiliary air valve that needed replacement. That part cost me 445 and 2 hours of labor. I had recently bought the car and the previous owner lived with this surging for years. I had a MAJOR tune-up and fixing of all leaks, etc. That cost over 4000. This aux. Air valve was the most costly part of the overhaul. (This was done in NYC)

Hope that helps because once they were done with my car, it was like new.

Good Luck,
Gretchen