Could someone identify/confirm that is a in-line check valve???

Looks very similar to this one http://www.ecstuning.com/stage/edpd/...productID=3022

And what is the funtion of this valve?

yes it's a check valve. it does what any other valve does, controls flow

yup, you should check all your other valves as well. if any of them are broken you have a vac leak. there's a guide on AW listing all the locations

yes, check valve. They only let flow go one way

That valve in my car looks about the same.... i know it's a check valve for the vacuum system but could it cause a boost leak? I've been boosting 1-2lbs under where i should be.

i dont know but i read in another thread that it could have made you boost low? im could be oh so wrong here. so dont go by me. but i know you can pick them up for like 25$ at audi dealers. people have been saying that there are four or so of them under the hood. the one thats near the airbox in mine almost has no grey rubber left! it looks all melted and crap....doea anyone know whow to install or is it a pull out and put in part? thats what it looks like..

I have to refer to jibberific's question here. Can that valve cause boost fluctuations or overboost?? How canI test it?

Turns out that my boost leak was from the vac hose connecting the intake manifold to diverter valve. It was cracked pretty badly and replacing it resulted in my boost going from 4-5psi to a consistent 6-7psi. Apparently the fabric-wrapped hoses can't expand/contract very well with temperature fluctuations and this can lead to failure.

Still curious what benefit can be had from replacing my old & cracking check valves... want to be sure they're worth the $100+ that it'll cost for 4 new ones

1stvwparts.com has these little guys for $20.34 and $9 shipping.