Just recently developed a misfire on my 1990 XJ40. Car only done 45000 and is immaculate, I only use it occasionally as my 2nd car though it has a run at least once a week.
The problem is on start up on idle there is a misfire, if I increase revs it gets worse though as it warms up the problem disappears, I can then drive it normally increasing my speed without so much as a hiccup.
I can leave it for an hour or so and same problem, it did get to a point where it would not start, left for few days then tried again it started with same misfire and symptoms as described above disappearing on warm up, if I increase revs having just started up the misfire is louder, and more often until warmed up.
Any help will be appreciated.