Mondeo 2.2 TDCI (175) - Cold Start Issue

Good morning all I'll try and keep this short but I doubt it sorry

I have a ongoing 6+ month problem with my 2009 2.2 TDCI (175bhp version) that hopefully someone has experienced before and can help me as i'm getting quite bored of throwing money at things it might not be.

The car when stone cold (e.g. sat over night / left all day, etc) can be a royal pain the bum to start. It has to be cranked on the starter motor for probably 6/10 seconds then it will start and fire out some dark grey/black smoke out the exhaust (it doesn't smoke abnormally any other time that i can see anyway)

This doesn't happen every cold start probably 1 out of 3 / 4 starts - it starts fine every time when warm or even if it has the problem then I turn it off straight away and then I turn it back on it will start fine.

I've taken it to some "diesel specialists" and one I left it for a week and they couldn't get the car to do it so got the "if we cant see it happen then there's nothing wrong with it but we've done a forced regen just in case please pay us".

on recommendations I've had the glow plugs replaced, EGR valve replaced, found a split intercooler pipe that I replaced, recently had a code for a low voltage reading on the throttle body so I replaced that aswell, but nothings seemed to of cured the starting problem.

I've also noticed a drop in low end performance recently car seems a little lazy so when I replaced the throttle body I cleaned the air intake temp sensor while it was out and it seemed to make the car more responsive but now its gone lazy again so i'll replace that for the sake of £14 but we shall see.

I still get 48mpg and it still goes OK. I've had the usual google search but nothing that absolutely matches my problem so I'm out of ideas now.

I've got the modified elm adapter and forscan and its clear of any codes so I have no hints there either.

Has anyone else had this experience?

Thankyou

Chris