I have major problems with my XJS 5.3 HE from 1984. I’ve messed with it for a long time without good results. It started with the last year being stalled and I got it driven home on an auto help. There was no spark on ignition so I started by replacing the amplifier, ignition coil with no result. I then started working more seriously and started measuring, finding that the pickup in the distributor was defective. I replaced it and the car started fine. The problem is that ever since it has had a choppy engine, especially when driving quietly. The degree of this varies, sometimes it’s quite a bit, other times I’m afraid the engine will stop. When I step on the accelerator and it has to work, it is very willing and speeds forward. May be very unwilling to start when engine is hot. Several people in Denmark have tried to help with good advice. I’ve spent oceans of time switching on ignition coils, amplifiers. Separate and clean power distributor. Tried to move the amplifier out in front of the radiator. All without result. Is getting a little tired of my otherwise lovely XJS. Just don’t know what to do. Hope there is someone who has had similar issues that can help me!?!? Don’t refer to Kirby Palm’s book, I simply don’t understand it. Not good enough. 
Thanks
Per
Have you tried changing the plugs?
I would renew entire ignition system if it hasn’t been done in a long while… Distributor cap and rotor, plug wires, and plugs. A general tune up.
In addition to what I have already mentioned. I also changed spark plugs, spark plug cables, distributor cover, rotor, both pressure regulators and gasoline pump. Are not 100% sure if it is petrol delivery or ignition problems-
Well, your shotgun approach is accomplishing nothing but emptying your wallet. Try this: With the car running, wiggle the wires coming out of the ignition amp.
Always a simple and good idea to try.
Seeing that the engine works well when accelerating or under load eliminates a lot of possible problems.
So we need to be precise about when you have the trouble.
- The engine stumbles under light load at any RPM ?
- The engine stumbles under light load only at low RPM ?
- The engine is hard to start only when hot ?
- Does it stumble the same when the engine is both cold and hot ?
- In what way does it stumble ?
Does it feel weak all the time ?
Does it feel good most of the time, but then every few seconds seems to miss ?
From the description of symptoms so far things that might need checking:
The plugs are gapped at 25thou.
The distributor pickup gap is correct.
The distributor advance mechanism is not sticking.
The distributor vacuum capsule is working.
The vacuum line to the fuel pressure regulators is not leaking or pinched.
The vacuum line from inlet manifold to ECU is not leaking or pinched.
The throttle operating rods, levers and bushes are good.
Maybe I have solved the problem, at least it has now run 100 km. without problems. I first tried the advice you gave me, but with no positive result. At sea I grabbed probably the only thing I haven’t touched, namely the trottle potentiometer. Removed in hopes that I could inject some contact cleaner into it. It was impossible so that is why I broke sealing over the three screws that held it together, didn’t really know what it contained and was afraid there were springs or something so it would break apart, without the opportunity to reassemble it. There were no problems, it was easy to separate. Immediately there was nothing that looked wrong. I cleaned, used contact cleaner, blew dry with compressed air and reassembled it. I had marked it before separation so it was easy to assemble it as it was before. Now drive the car as it should, hope it stays with it! Thank you for all the hospitality and the good advice. Greetings from Denmark, the oldest kingdom in the world. Definitely worth visiting!