Jaguar Repair: 86 XKS V12 will not rev, vacuum gauge, vacuum test

Question
Hi

I have an 86 XJS when the engine warms up it will not accelerate.
It idles fine about 800-900RPM.
When the pedal is pushed it jumps to 1600 then back to idle back ant fourth.
I would think this is an electrical problem not 100% sure though.

Answer
Hi Buck,
A no rev up condition can be many things but you need to do some testing. First run vacuum test and open the throttle very slowly and watch the vacuum gauge and tell me what it does. If it goes to zero very quickly I would check exhaust back pressure first. It should not run over 1 and a half PSI as you try to rev it up. If that is ok spray some fuel or WD-40 works well, into the intake while someone tries to rev it up. If you have less than 1.5 PSI back pressure and it revs up with a spray, then it is an injection problem and will require several tests. First being a fuel pressure test. Let me know,
Howard