The car vibrates slightly on idle in park or neutral, nothing massive but you can feel a trembling going through the car. It only does it when stood still and goes away when driving or revving the car. No front end knocks can be heard at anytime.

Could this be the engine mounts, the reason I ask is I also have high LT and ST fuel trims and I understand this can cause a similar thing. However the car always shakes when stood still whether I'm in open or close loop, when cold and engine idle revs are higher it can be felt more than with a hot engine and lower idle engine revs. Both idling speeds are smooth and constant.

Any ideas??

 

I'd be looking for vacuum leaks first.

 

Vac leaks cant be found so far even with a smoke test. Fixing the trims isn't going to be easy, just wonder if this was the cause of the idle vibration or if it could be the mounts.

 

As you have a fault that does cause that I'd fix the known fault rather than assume there are multiple faults.

 

there tend to br vacuum leaks at the brake booster line at throttle body collet oring. they fall apart with age. i found mine by spraying it with carb cleaner and a smoke test to confirm.

I hade a wierd idle and high fuel trim before replacing.

 

Dont think Ive checked this area, at least it doesnt sound familiar. The throttle body rubber ring does feel a bit suspect, but increase pressure down on intake elbow onto the throttle body makes no difference to the trims, and it does seem to fit snugg round the intake and throttle body. Plus I would have thought above all the Jag specailist would have found this.

 

Well, if you have high fuel trims, it is likely you either have extra air getting in or low fuel pressure. The X-308 has a fuel pressure test port and test gauges are cheap.

BTW, I found my air leak to be the front main oil seal, believe it or not!

 

Doubt its the fuel pressure the car does around 17mpg, using plenty of fuel.
Performance is good, very good since I fitted nameless Cats and custom exhaust.
No codes of course, I do however have a minor oil leak, not sure if this is engine or gearbox, so small I've never looked as of yet.