Originally Posted by hrc4u

the thing in filter housing seems to be an "intake air switch over valve" ...the official manual says nothing in maintenance section about cleaning that one (neither have i ever cleaned that)
the Audi training manuals says this about it:
'"If the engine requires a large amount of air, the
engine control unit (active opening) activates the
solenoid valve N335 and a vacuum modulator opens
the wheel housing inlet.
The passive opening of the wheel housing inlet is
activated if an excessively high vacuum is created in
the air filter housing (e.g. obstruction of the intake
opening at the front of the vehicle). The increased
vacuum forces the flap of the wheel housing inlet
open.
The raw-air intake system is fitted with an additional
intake pipe from the wheel housing with flow-optimised
cross-sections."

cheers/H