IloveSSSS

I just did a pressure test on my 2001.5 S4.
At 5psi, all the air is coming out of the small hose that is connected to the big hose between the MAF and the Y pipe (the one that is a bitch to disconnect. No idea what's its purpose or name).
Seems like something is not closing the way it should. I checked the bypass valves and they are OK.
I have no clue what to test/replace next.
any pointers?

Thanks

DAP@EPL

That's the brake booster line.

visintainer [vis]

jb weld it back up

IloveSSSS

<center><img src="http://pictureposter.audiworld.com/46939/dsc_0010.jpg"></center><p>Is it the piece (Arrow) that connect to the main hose (between MAF and Y pipe) that is suppose to prevent air from going backward.
If so, anybody knows what's the part #.
There is not much written on it beside KYS made in germany and Motor

visintainer [vis]

<ul><li><a href="https://forums.audiworld.com/s4/msgs/2784689.phtml">https://forums.audiworld.com/s4/msgs/2784689.phtml</a</li></ul>

b5s402

2nd..

ErikS4

your crank case.