Cold "stumble", off idle...?
Discussion
Normally when you lift the cluth you also open the throttle. If it's really lifting the clutch that causes it (i.e. you hold the engine at fast idle on constant throttle, ease the clutch up and it dies) then there's something funny going on. My guess is it's more likely to be caused by opening the throttle, and if so you will probably notice hesitation when you blip the throttle at low revs too.
Assuming it is caused by the throttle, the most likely causes for a misfire under those conditions are overfuelling or a weak spark. If you had a damp engine bay I guess it could be damp leads drying out as the engine warmed up, I don't think this is very likely but you could prove it by starting the engine from cold at night with the bonnet up (stray sparks will be very obvious!) and WD40 will probably cure it.
I suspect it is more likely the cold start enrichment combined with a rich base mixture pushing you slightly too rich. It is worth checking the fuel pressure, if somebody has helpfully tweaked the fuel pressure in the hope this will improve the power then this could be the cause. Alternatively it could be a weak spark, a spark trace would confirm this, if so it could be that plugs or some other ignition component need attention. Or it could be under fuelling. Or a duff throttle pot. Or a faulty earth, or a failed coolant temp sensor, or ...
Whatever it is, a well maintained car shouldn't do it so it is worth mentioning at the next service if not before.
Cheers,
Peter Humphries (and a green V8S)
Assuming it is caused by the throttle, the most likely causes for a misfire under those conditions are overfuelling or a weak spark. If you had a damp engine bay I guess it could be damp leads drying out as the engine warmed up, I don't think this is very likely but you could prove it by starting the engine from cold at night with the bonnet up (stray sparks will be very obvious!) and WD40 will probably cure it.
I suspect it is more likely the cold start enrichment combined with a rich base mixture pushing you slightly too rich. It is worth checking the fuel pressure, if somebody has helpfully tweaked the fuel pressure in the hope this will improve the power then this could be the cause. Alternatively it could be a weak spark, a spark trace would confirm this, if so it could be that plugs or some other ignition component need attention. Or it could be under fuelling. Or a duff throttle pot. Or a faulty earth, or a failed coolant temp sensor, or ...
Whatever it is, a well maintained car shouldn't do it so it is worth mentioning at the next service if not before.
Cheers,
Peter Humphries (and a green V8S)
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