1.6 turbo diesel
Stone cold. first startup in roughly 24 hours. Temperature around 3-4*c (~37*F?)
Was kept in the garage overnight and up until I was about to start so the engine temp would be a bit warmer. The engine has a fresh rebuild on it (done by a shop and timed by the shop)
This start was without the cold start lever pulled out. but was pulled out shortly after (lumpy idle)

Then there is this miss when running...
(evident by the puffs of smoke)

Being stone cold I am not as concerned about the ammount of smoke, the lumpy idle/miss is a pain but if it can help with the diagnosis I'll toss it in there....
What has me concerned is that I can have the engine up to operating temperature, let it idle for a few minutes (long light) then snap the fuel to see the white smoke.
Having done a search here I'm led to believe it's timing since the coolant hoses don't develop rapid pressure.
Any signs of fuel leaks, or sucking air??? Were the injectors redone during the rebuild???
No, injectors weren't done during rebuild. I am getting four injectors rebuilt by Giles. Just waiting to get them back...
No immediate sign of fuel leaks but I should go back over the fuel system from front to back. I should also install a section of clear hose...
See how it does with some new injectors.. Amazing the difference it can make.. My one car acted much the same as yours with the addition of what felt like a bad spark plug wire at cruise.. Injectors made it a whole new beast...
Check your fuel system anyhow, it can't hurt...much. A section of clear line is priceless!!!