The car: 1985 5.3V12 Coupe - 56K miles.
The key turns, a momentary buzz from the fuel pump and the start is without hesitation. All 12 are running as one and the idle RPM sits at around 1200RPM.
The first 4 to 5 miles is like silk, power and acceleration is faultless - and then, a tweak of the throttle and the first, slight hesitation. A stop at traffic lights shows RPM still at around 12-1300 RPM. The remainder of the journey is ‘blippy’, the hesitation becoming a little more frequent, noticeable and longer-lasting with every press of the accelerator. Destination is reached (phew!). Average fuel consumption from the trip computer went from around 15 to 11 by journey’s end.
The return is a more traumatic. After a clean start, the RPM is up at 1500RPM and the hestitation is turning into a progression of lurches within a few hundred yards of start. The best speed I can get is around 25 mph with RPM cycling between 500 and 1500 RPM. I reach the point where acceleration is almost impossible. I pull over.
After 2 mins I start again, RPM goes up to around 1500 then slowly comes back to around 1200, and off I go. Acceleration is a bit better, I can sit at around 45mph but there is a ‘blip’ with every press of the accelerator.
The final turn into my road requires slowing to around walking pace and as I lift my foot off the accelerator, the engine dies. Immediate restart - dead. A start 30 seconds later; a good start with the now characteristic 1500 RPM and I make it home.
So please, all you XJS Sherlock Holmes out there, what does the mystery suggest to you and what is the villain(s)?