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ISV Check-Valve for 1990 VW Corrado


I recently purchased my Corrado when a friend gave me an offer I couldn't refuse.  It wasn't perfect, but, it has potential.  I'm waiting for my Neuspeed chip to arrive in the mail any day now, but, while I was waiting around for the order, I decided to address one of the most popular sources for a loss of boost in the VW G60 plumbing... a leaky ISV (Idle Stabilizer valve.  Below is a picture of the ISV and routing on my '90 G60 Corrado.

A schematic of how the check-valve would operate is shown below.  When air flows towards the ISV, it is unimpeded by the check-valve.  But, when it tries to flow in the opposite direction (boost leak) the ball will seat against the rubber washer and create a seal.