The problem started with my 87 XJS Cabriolet [V12] last year after I pulled it out from winter storage.
The car starts without problem and it runs perfectly at 700rpm while is still cold, I can even rev it up to 2500rpms without issues. But the problem starts once the engine reaches warm up temperature, so as I step on the gas and the tachometer reaches +/-1300rpm the rpms start fluctuating between +/- 1700rpm and +/-600rpm nonstop until I release the gas, and at point the rpms settle at 700rpms and the engine idles smoothly again. This problem is constant and has rendered the car undriveable. I know it sounds like an issue caused by a defective Auxiliary Air Valve, but the AVV isn’t the problem.
This is what I have tried so far:
- Auxiliary Air Valve [Note that I tested it before ordering the replacement, which was working correctly, but since I had replaced it back on 2011, and to be on the safe side I decided to install a new one].
- Fuel filter
- Fuel pressure regulator [outlet side]
- Distributor cap and rotor
- Spark plugs and wires
- Battery [The old one wasn’t holding charge anymore]
Injectors were serviced 5 years ago.
B. CHECKED / ADJUSTED:
- Vacuum advance leaks [All the hoses and connections looked fine and secured].
- Throttle disks and linkage.
This forum and Kirby’s book are always my first sources of advice and guidance; however, this time I haven’t been able to find the solution to this problem.
I really hope you guys have an idea about the potential cause and solution to this issue, which is driving me crazy [no pun intended].