Could someone enlighten me on what this valve does exactly? It' located on the intake hose. If it went bad, would it cause boost problems similar to a faulty n75 or wastegate?

 

Vents your crankcase to the turbo inlet. Called the pcv system. Delete that **** and get a catchcan.

 

so this acts like a filter??? and how do you know when its bad?

 

Not exactly, it just regulates when it allows vapors thru it. Like when the turbo is sucking in a lot of air, the valve is open and pulling the excess air and oil vapors out of your crankcase. Problem is that its pushing oil and crap thru your turbo, which obv isn't good. You want nice fresh air going thru it. Most people delete the pcv system and run a catchcan instead. It's debatable whether you should have the pcv hooked up to the catchcan or just have a filter on the catchcan to vent it to atmosphere, but imho, a vented catchcan that's mounted high is perfect. A bad pcv valve (or pancake valve) would be cracked and leaking oil out of it. If you saw how much oil accumulates in a catchcan, you'd never allow that to go thru your turbo.

 

how much are those catchcans you conveinced me =D

 

I am now enlightened. Thanks for that info!

 

This is on my list of things to do eventually. Andrew, you can DIY for cheap. eBay has decent stuff. Check out this thread:

http://www.audifreaks.com/forums/showthread.php?t=756

EDIT: Thought it was worth adding that, if you couldn't tell by the pictures, that DIY was for the MkI TT, which has a transversely mounted 1.8T as opposed to ours which is longitudinal. I linked that thread more for the explanation and information it contains, not so much the installation guide. I'll see if i can find a good DIY for the A4

 

You shouldn't use a vented catch can because it will let in unmetered air.

 

Its also bad for the whales and trees and baby seals and whatever else the hippies are trying to save these days

 

thanks buddy looks pretty intresting!