Intermittently bugged 290 GTD engine (602 983)

With reference to my previous post regarding this intermitted starting problem and the EDC light coming on inidicating a loose connection on the main harnass cable - it was then fixed but low and behold - about 2000km later - two recurrences in a row and then all ok again?

Now i have this smoking problem.I have lately noted some intermittent black smoke, seemingly most often after driving at highway speed for a while and then stopping say at a traffic light, sometimes when idling and once whilst coasting and then accelerating. After idling a while the smoke disappears again. When I noted the smoke while travelling it also disappeared after a short while. Whilst driving i could not feel any change in performance, nor when pulling away while it is smoking. Should i be concerned about this - it has never smoked this much? The engine was bought new from MB, installed by them and has only done about 35K km. The old computer and accelerator unit etc was however used. All other important things like IP and turbo came new with the engine.

I have read about the ALDA sensor and is aware of the boost pressure sensor on this engine, but what could the cause for this intermittent smoking be? I have checked the air cleaner element and is clean, and the boost pressure sensor is connected and the pipe from manifold is in tact. Could this problem by any chance be related to the starting problem which also seems to be fuel related? What i am thinking about is the accelerator unit (rheostat?) sending varying information to the IP causing over fuelling?

From now on I will refer to this engine as the intermittently bugged engine

any wisdom will be appreciated

Regards

Freek