Audi A6 C5 airbox hose?
 

Anybody know what the disconnected hose on the front of the airbox might be for? I'm guessing some sort of breather pipe - it's got an O ring on it and is a push/twist fitting.

http://forum.a8parts.co.uk/attachmen...1&d=1362319623

I'm guessing it was removed when the air filter was last changed about 2 years ago (not by me!) - only spotted this as went in to change both headlight bulbs this pm.

If it is a breather pipe will it have caused any issues being disconnected long term?

Glad it's tucked away behind the headlight so unlikely to have sucked anything much in there.....

All I can tell you it's not there on our 2.5TDI.

Lol - yeah, it's a 3 litre petrol :)

Is it an alternate hot or cold air intake (depending where it originates)?

Looks like it goes to secondary air pump. I don't think there was any harm done by it being disconnected as it only blows air in exhaust when engine is cold and running rich to burn up excessive hydrocarbons and heat up cats quicker.