2003 a4 air intake question
 

hey, i own an audi a4 b6, and im just wondering what is the other tube going into the air intake maybe a inch in diameter, what exactly does it do, sorry for the newbieness and no im not talking about the one thats hooked up to the turbo the smaller tube. please and thanks

Re: 2003 a4 air intake question
 

Don't know for sure but could be part of the PCV system to recycle blowby gases from the crankcase and valve covers back into the main air inlet stream.

The other tube I think into the air intake would be for the secondary air inlet pump that is used briefly during cold starts to add more air/oxygen into the intake stream to help get the catalytic converter up to operating temperature quicker.