Bad n18?

Should N18 hold vacuum?

With regards to N18
The line feeding the VAC (top nipple) is providing 28 inches per Mityvac.
N18 WILL NOT hold vacuum
I pulled it off and tested both ports...I would run it up to 20 inches and it just slides right back to zero.
N75 and N239 held vacuum.

PROBLEM THAT GOT ME HERE:
Low power/ boost when car has been running 15-20 minutes.
When car is cool, runs like a champ, boost climbs steady to 15-16 pounds no spikes or jumps.
When been run awhile, boost wont go over 6...
Turbo and actuator (newer) pass bench test, actuator works great, vanes move freely.
Borrowed MAF from pals great running TDI. no change there.

I'm going to order vacuum hose line kit and am wondering if I should order another N18 as well? This issue has me scratching my head a bit.

Thanks in advance!

I like having spare parts either way, I would.

Should be able to swap n75 to test for operation first

I will go ahead and order but I am trying to avoid throwing parts at a problem vs tracking down the actual culprit.
Should the 18 hold vacuum? I figure it should

i say yes; just off the top of my head I'm thinking these should be normally closed valves that allow vacuum through when the computer tells it to in order to regulate boost and EGR operation. meaning of course with power off, they should hold vacuum.

http://forums.tdiclub.com/showthread.php?t=419530

this thread has some details

If the vent hose from the vacuum valves is left off the airbox, dirt can enter the
valves and cause problems.
I was able to blow some debris out of my N75 with an air nozzle.

May-39 said:

Should N18 hold vacuum?

With regards to N18
The line feeding the VAC (top nipple) is providing 28 inches per Mityvac.
N18 WILL NOT hold vacuum
I pulled it off and tested both ports...I would run it up to 20 inches and it just slides right back to zero.
N75 and N239 held vacuum.

Click to expand...

My N75 did not hold vacuum on any port (blocking the other 2)
I sprayed a little WD-40 in the ports, shook it, and lightly blew air in each port.
My performance seemed better for a few weeks but now is back to intermittent slight loss.
I do not know the internal design but I suspect it has reed valves or such.
I have to order a timing belt kit and that's on the list also.
Haven't tested my other valves.
MPG was a bit higher also.