Hi Starbuck,
once again many thanks for your detailed answer! I wish someone like you was around here in Germany so I could consult him, but unfortunately I haven't yet found someone with accurate knowledge and commitment.
I had expected to find some mech here that would make a list like yours and work it through, but that's obviously asked too much. If they can't use their books and reference charts or electronic diagnosis system, they are lost. At latest they run away when they hear Jaguar V12 (for some, 'Jag' is already enough). The best offer was: 'Leave it at our garage for a couple of days or a week and we we will see, what we can do about it'. I would say a Pro should be able to work through your list in half a day or one day at most, do you agree?
I will see what items of your list I can check on my own and for the others I will try to get professional support. There are two things that have already been checked/done:
- the spark plugs have been replaced recently, drove about 800km with the new ones. I could have a look at them and see if one or several of them are more or less sooty than the others.
- fuel tank and pumps have been checked last fall (because there was water in the tank), fuel pump relay had been identified as single source of error (car wouldn't start)
A stuck valve sounds serious - I hope it's not that.
Best regards
Oliver