Mass/volume air flow A circuit range/performance error (P0101)

[Nils]

Engine light is on and the computer gives this error. I have tried to change the air mass censor but that didn’t help.
When I first start up the car it smokes very much (black smoke). And after some minutes of driving it loses much of its power and the smoking stops.

I would very much appreciate some tips

Car: Subaru legacy 2.0 (2009)

 

[Ecmbuster]

Intake air box is clean and clear?
Engine coolant temperature is relative?
Intake air temperature is relative?
No Exhaust restrictions?
Fuel quality?
Injection pulse width is relative to temperature and RPM?
MAF reading is relative to RPM and engine load?