[Piwoslaw]

Found more onfo on how the air doser works:

The airflow can be restricted in two places: one ("warm air doser", WAD) is between the 'to' and 'from' intercooler stretches, this is normally closed, forcing air through the IC. Second ("cold air doser", CAD) is on the exit from the IC, this is normally open.

When starting a cold engine, the WAD opens to allow warmer air into the engine. Once the temperature rises, WAD closes, directing air to the intercooler.

During normal operation, when exhaust gasses are recirculated into the engine, the WAD is closed and the CAD is partially closed, restricting the amount of air that goes to the manifold (also, the variable turbine pumps less air, I'm guessing). This reduction of air pressure in the intake allows more EGR to enter the cylinder.

When the diesel particulate filter needs to be burned out, the WAD opens again, helping to raise exhaust temperature.

I read that in early TDI's a similar set-up would close both valves when shutting the engine off. Supposedly, blocking the airflow was safer than having a rush of high pressure air hit the suddenly stopped engine. Maybe this is still the case in newer versions of the TDI, and the HDi.