I am also diagnosing an issue with my vacuum system and the bypass valve. I can blow through the solenoid from the bypass valve vacuum line with the car off. I contacted the manufacturer Pierburg and asked how to diagnose these. They kindly replied to me with a pdf which describes the procedure. I have taken a screen shot of the relevant portion because the file is too large. It seems the top of the solenoid should be sealed, and no air escapes when powered off. When the solenoid is activated, there should be flow from the lower two in any direction, meaning to the vacuum tank if I am not mistaken Image Unavailable, Please Login
