Thanks for the ideas guys.

ABS light is not on.

I have not changed the OVP unit. Anyone bought one recently and know how much they cost?

Cranking time when cold is under 1 second before engine fires (well, the coldest it ever gets here is -5 ish).

It passed the MOT last year with the eratic idle, so I suppose it should pass now. There doesn't appear to be any smoke. I may take it to Diesco (diesel injection specialists). Mercedes dealer doesn't seem to know anything about this engine. Could a dirty fuel filter cause this also?

I know it's a non-turbo, but I'm pretty sure that it should be a bit more powerful than it is too.

Many thanks,

John