Have we got any diesel expert out there, got a problem with a Citroen Dispatch 1.9TD XUD engine.

After rebuilding the top end of the engine due to head gasket failure I now have smoke on idle and low revs, if I take the van for a run it clears but as soon as it sits for 30 seconds or so it starts smoking again.

It seems to me like it's overfueling, but can't see that I've changed any settings.

Head has been fully checked, valves seats redone etc. Engine has good compression and seems to drive fine.

Can't see that the diesel timing is out as I've checked it a couple of times now.

Smoke seems to be white/grey and then black when you rev it hard, clears after a rev or two.

Had one little plastic bit left over in a pot and I'm not sure what it's from, thought injector, but can't see where it would have come from. May just have been in the pot already but I don't think it was.

Pics below:

Anyone got any suggestions, it's passed the MOT fine, but just seems to smoke after sitting for a while.

that part looks a bit like the drive peg for the servo pump?
as for smoke,white is usually water,maybe left in exhaust or brake fluid

it might need the pump setting fiddling with if its been messed with.
these can be quite picky about settings as i found out just by fitting new injectors on my ZX TD
don't recognise the part you have left over though.

white/grey smoke can mean turbo issues though

black is usually overfueling or un burnt fuel which again could be pump setup
did u have the injectors serviced when the head was stripped? and does the idle become uneven when you start getting the smoke?