This is Alfa Romeo Giulietta installed oil separator. Disassembly shows the vent is guarded by a flat rubber circle pushed up by a spring. This rubber flab probably ensures the air only flows in. Other than that the separator is connected to the engine block for oil to drip, and has two hoses: one leading to the intake hose before turbo charger and the other probably to the crank case. Why would it have this vent in the cover?