mine was much as yours, first got it serviced but only anoil and il filter change as only done 7-8 ooo since last service, jaguar recommends servicing every 16,000 for the xj. but I wanted an oil change. its all in town driving that I do, very low mpg 30mph if lucky. after the service , when picking the car up it felt roughf, making me question the dealers in m head, ( it feels rougher than I gave to them ) after only 2mile or so, pulled into filling station put oxicat in tank filled up after nearly 2weeks felt it kicking in, that tank full has gone, down to a third then filled up BP ulti car so smooth , no more turbo lag, I even drove to work to day using the paddle shifts falling back then foot down great . I have 3 cans left add another one may -june . mine oly done 44000 but turbo was neading cleaned out as I have noticed big time. glad yours is doing fine to . james