E53 2006 4.8is rough idle cold start - help required

[Hugo74]

Hi All,
I own a X5 2006 4.8 is with 195000km (N62 V8 engine double Vanos).
I have a rough idle at cold start which go away after 40 seconds, but when i drive the car, the engine sound is weird and the behavior/power of my BMW is not like before... yes... by before I mean the following events;

Got oil level check light some weeks ago, some weeks after doing my oil service... brought back to the workshop, they found 2 major oil leaks (not seen at time of service... anyway) + lack of coolant (coolant expansion tank cracked). Note; I did not get any light on my dash board for the coolant.
Got my cylinder head cover gaskets and the upper timing gaskets replaced (both banks), coolant expansion tank, thermostat and some hoses replaced.
Got back the car...the first morning at cold start I had a rough idle, but the ignition was correct (cranking time very short), I have the rough idle after 3-4 seconds, after 40 secs approx, my rpms go up 1000 and come back to 500-600... no more rough idle then.
But the engine is not ''singing'' like usual, the behavior is not like before, no power, my car is now a lemon.

Back again to the workshop to find the root cause and to fix it;
- Vanos codes 2A84 and 2A89
- Misfiring codes but did not come back after deleting faults codes and start again the car when warmed-up
- No coil/sparkplug fault code
- No alternator/battery fault code
- camshaft positionning found to be correct after adaptation programming.
- we replaced both Vanos solenoids on bank 2: No positiv result
- We replaced 8 injectors: No positiv result

Questions:
- During the gasket replacement, according to you, what could happen? sensor broken or wrongly placed, damage on Vanos or eccentric/camshafts?
- Since I ran with no coolant for a while, did I burn some gaskets which are now allowing some coolant entering into cylinders and cause those misfiring?

I already read many threads about misfiring at cold start and rough idle like mine, but there were so many possible root causes...
I'm lost, my mechanic seems to be as well...
any help from you guys will be appreciated

Thank you