So for a couple of weeks now it's been this way. When it first started running HORRIBLY rough at idle, it scared me thinking something was seriously wrong with my 2001 1.8T A4. After some poking around I noticed this thing "open" and pushed it together to find that the rough idle completely stopped. I pushed it together and then eventually it would pop back open. Every time I try to pinch it closed, it pops back open and rough idle continues. Is this a common issue and what do I need to do to fix it? This valve/vent is located to the left of the coolant reservoir behind the intake manifold.

 

Nevermind.... I just saw this same thing about 5 posts down. What a coincidence!?