My ‘84 3.6 XJS is currently changing mood constantly.

I can be driving with everything working fine - and suddenly, it will not idle - every time I press the clutch, the engine will just die. Eventually, the problem will disappear and the engine will run perfectly fine again.

When the problem occurs, the engine gets very jumpy at low revs.

It seems to be happening regardless of engine temp - and I cannot find any other things that it could be related to.

I hope that some of you might have ideas where to start diagnosing the problem?

 

I don’t know anything about the AJ6, but this problem intrigued me so I went looking for an answer. It sounds similar to this problem, although I may be totally wrong. A COMMON PROBLEM WITH THE EARLY 3.6 XJS (1983-87) / AJ6 Engineering

 

That old problem of rich idle has presumably been fixed in your car years ago, Tim? Does the idle get bad by itself and then pressing the clutch causes enough extra load to stall it? Or is the idle only bad while the clutch is pressed? Do these cars have servo-assisted clutches?

I'm trying to work out a slightly bad idle in my car, but it sounds like there can be many causes - gunk and carbon in the intake, vacuum leaks, oil in the spark plug wells, rich idle in earlier cars, and all the standard stuff like bad sensors and electrical connectors and injectors..

 

Thank you both for your replies!
I think that the rich idle problem seems plausible - the article which was linked to above, describes both that it won't idle and that the engine seems to jolt when at low revs in gear - but I am not sure of I can verify whether this is actually the problem before spending £300 on solving it?

Other threads on similar issues talk about the idle air control valve, but I am not sure whether that is in any way likely to be the problem...?

The engine has just been serviced, so I am assuming that a lot of the potential problems should be solved - but maybe I should spend a full day on clean all connectors around the car...

 

I'm not sure whether your car has one or not! Mine does, but it's a later 3.6 which runs a different ECU than yours, and I believe there were various other changes to the engine management. It's hard to find info when every search turns up the Auxiliary Air Valve for the V12.

Maybe you could get your car's exhaust CO levels checked before spending that £300?
Someone also pointed out to me that the Jaguar XJ40 (XJ81) section of this forum would have more info on our AJ6 engine.