XJR 1999 rough idle help!

[jaghead69]

I just love my XJR, it's 4.0 supercharged 1999 with about 88k miles. The problem started yesterday on a long run back from the south east coast. Stopping at lights etc it started to rough idle. Them when pulling away it will die, some times it will pick up but some times it cuts right out. Mph on the 200 mile run was 13mpg. Once going it runs well but then on stopping it starts to play up again. Also very smokey exhurst, and dark in colour. No fault codes showing. Anyone had this problem? I am not very knowledgeable on cars!

[P700DEE]

13 mpg says you have a serious fueling problem. You should get about 20mpg+ on a good run. Get the codes read its not well

[Jaguar steve]

What P700 said. Heavy fuel consumption, black smoke and heavy exhaust deposits suggest it's running seriously rich.

Excess fueling will eventually Muller the engine. I'd get it sorted asap and once it's fixed change the engine oil

[jaghead69]

Thanks Guys, Have booked it in to a Jag garage off the Purley Way in Croydon. Have heard good reports about the garage. My Son also has an XJR and he said it could well be a Lambda sensor? Will post a result!