Misfire and clatter - but not all the time

[Johnno]

Help needed in diagnosis on some strange symptoms. The car is a 2.1TD VSX Xantia. Recently, it has developed two symptoms. A misfire which started some four to five weeks ago on a trip to Southampton, went away and is now back. Earlier on the same day, the engine suddenly developed a pronounced clatter and went rather dead - as though the timing had slipped. This went away after I decelerated (well, you would, wouldn't you!) and then gently re-applied the throttle. The clatter still occurs from time to time, but neither symptom is consistent. The misfire doesn't occur under hard acceleration and the clatter can occur under no-load conditions. There is no apparent air passing through the pipe into the pump and both symptoms may be completely unrelated, as they haven't occurred at the same time. I have considered the electronics on the pump, but this is difficult to check, and because of the lack of consistency, you just know that the beast will behave in a workshop! Could the pick-up on the flywheel be the culprit? The timing belt was done earlier this year. Additional info is that the idling is smooth after coming to a rest, but after a few seconds becomes a little 'lumpy'. On start-up, there is often a quick surge before settling down.
Not much to go on, I know, but some of you may have come across this sort of thing before.
Cheers,

[jeremy]

Have a good search of this site - 2.1 sensor brought up loads.
try this one for size
http://www.andyspares.com/discussionfor ... IC_ID=8985
jeremy

[Kowalski]

With older diesels this sort of thing would either be injectors sticking / dripping or a fault with the injector pump, these tend not to be intermittent. A classic symptom would be that the engine would smoke while it's being noisy.
The 2.1 is electronically controlled so Jeremy's suggestion sounds plausable electronic faults can cause you no end of grief...