Mike S

OK...I need help. I've been chasing down an elusive vacuum leak (i'm told that's what's causing this) for weeks now to no avail. The car will start and runs well above 2k(boost is a bit slow to build for stock turbo), but it won't idle. Idle fluctuates from near dying to 900 rpm....after about 20 seconds it will stabilize out, but its idling low...around 700rpm.

I've dissassembled and reassembled the intake about 5 times now. All hoses have been replaced except for the really long one going to the cycling valve and oil separator. On my car the PO had the blow off valve venting to the open air. I noticed that the stock BOV was torn so I replaced it with the 993 unit. That unit seems to be sucking in a small amount of air at idle. If I cup my hand over the bottom of it the idle comes right up and stabilizes....same thing happens if I unplug the vacuum line going to the BOV. Thinking I got a bum valve I bought a stratmosphere adjustable one....same problem with that one too. Is this causing my leak? How do you guys vent this to the atmosphere without having a vacuum leak and why didn't I have problems before?

Mike S

OK...found something in the archives. Turns out the stock valve can't vent to the open air. It leaks air at idle. I would have thought the new stratmosphere one would be able to...but it can't either apparently. Not sure why my old valve was ok....but looks like i'm going to have to reroute it to the intake like it was stock.

nine-44

What is happening, is , at an idle, the stock bypass valve is open to vent the boost. At an idle, the valve(when not comming out of the throttle) is pulling unmetered air in. This is causing the problems, you can get a blowoff valve that only opens under mild boost or higher. Thus, at an idle, it is not open to pull air that is not metered. The Stratmosphere valve can be adjusted(if you get the adjustable one)to only open on boost conditions and stay closed when there's not boost to releive.