sayporsha

I paid $25 for a new OE replacement valve from a local repair shop. I'm running 16# boost and it's holding up just fine.

Matt H

It will hold up just fine for some time. It will however, fail, at some time as well.
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Danno

I'm always for the AND solution as opposed to EITHER/OR. So.... if you examine the vacuum diagram (Wayne Greham's), you'll see that the bypass-valve experiences positive pressure when the car is under boost. This boost actually helps push down on the diaphragm and keeps it shut. Then when you let off the throttle, the bypass valve will get vacuum and open up. This then vents the two big ports through to teach other.

So the test would be to BOTH suck and blow. Sounds like you have a bad bypass valve, but it shouldn'thurt too much. Just slows down your turbo a little bit more than stock on shifts. And it'll cost you 1-2psi of max-boost. Not all that gruesome really. The really bad part when these things fail is the turkey-like gobbles it makes under your hood when you let off the throttle. Makes people on the sidewalk take a wnd look to see if you've got turkeys running on treadmills under the hood...