lumpy idle

hi guys, any thoughts appreciated :

1997 dse sometimes lumpy on tick over had the fuel pump replaced no difference, checked all electrical connections etc.

i now have it in mind that the problem could be hydraulic tappets with a bucket not pressurising ie not acting on a valve as maybe it should.

the problem is only on tick over and not consistant apart from that the motor runs sweet as a nut smooth as silk

your thoughts always appreciated

could it be whatever controls the idle mixture/rate? i know very little about deisel but thats what i'd be looking for on a petrol.

know wot ur saying and i would agree had i not had the fuel system completely checked out by injection specialists even to the point of them sending the fuel pump that was fitted new back to manufacturer to be fully checked for faults ! i am now 99.9% sure that the fuel system is functioning as it should

how much dampness are we talking at idle? Does the needle on the dash move more than a millimeter when at idle? I have had 4 diesel cars all 6pots ranging from new to 12 years old, and they all have a tiny bit of dampness at idle.

at a guess id say it was only firing on 5 its that noticeable ! but like i say it is sometimes perfectly ok probably at its worse in traffic and sometimes a blip on the throttle cures it, the tickover speed has been increased sightly to help negate the problem and at idle speeds of 1000rpm the lumpiness disapeares all together, i am fast going bald where ive been scratching my head

It sounds like my engine, though i wouldn't call in lumpiness, just a heavy vibration at idle, like a lot of diesels do. I consider it normal, though no less annoying.

If I get the revs over 800 rpm it is smooth like you say.

I've always wondered where this vibration comes from, i suspect its the serpentine belt tensioner, or the crankshaft pulley.