Cylinder misfire fault codes

[Tailsme]

I have noticed recently when I start my X-350 when it already has a fully warmed up engine, I sometimes get a rough idle and the occasionally the engine light comes on in the dash panel. I have read the code faults and it is always cylinder misfire on 3, 5 and 7. When this first happened I tried putting a fuel cleaner in the fuel to clean the system but about 2 weeks went by and it happened again, I again cleared the same faults and now about 3 to 4 weeks later it has happened again. This only happens when I first start up with an already fully warned up engine and if I rev the car for a few seconds it clears and the idle goes back to normal. Any ideas when my problem is? I am wondering if it is dirty injectors or maybe the throttle body but it is always on the same 3 cylinders. Look forward to any comments.
Thanks
Darren

[robv12]

I am assuming here we have a petrol V8??. mileage??

you say you have read the fault codes, but have you had the car scanned on a Jaguar or Autologic system, that gives the fault rather than just the code

if you have and it is pinning it down to individual cylinders, I would suggest a look at coils and plugs as a first port of call

you may also have a split vacum pipe, I had this on my XJR took ages to find

[ptjs1]

Tailsme,

Are you getting codes P0303, P0305 & P0307 at different times or do you get them all being flagged at the same time?

If they all come together, you might look at the oxygen sensor on that bank, even consider a catalyst problem or just check the wiring on that bank.

If you get the fault codes separately, then individual coil packs may be an area to consider.
As Rob says, you might want to get this checked by a dealer or independent who can verify in more detail the fault, particularly if you can induce the problem to happen whilst at the specialist.

Good luck

Paul