What is this piece? usage? zb 7502021
 

Going through my engine bay and have always seen this piece. always wondered what it's for.

the number on the piece is zb 7502021 bmw.
I have the 3.0i; it's on the left side of the engine
looks like the following;
http://i.ebayimg.com/t/BMW-E53-OEM-E...VhUMV/$_57.JPG
:dunno:

It is the intake for the SAI (secondary air injection). It is air injected into the exhaust to help with emissions on start up.

thank you !