Originally Posted by marmite
only when falling from high revs.. what is the bpv... ?
Turbo Bypass Valve - it releases air pressure from before the throttle plate when it closes (ie when you let off the gas) after being in a boost situation. It's located at the front of the engine on the left (if your looking from the front) side of the flywheel cover, attached to the rubber joint on the intake inlet on the turbo. It is kind of a pain to get to, because you have to spend a few minutes taking off all the turbo piping to get to it. It has a tube that goes over to the throttle body, and a vacuum line to the intake manifold. If you suck on the vacuum line connected to it and find it is not able to hold vacuum, it isn't operating properly - it is both leaking vacuum and not doing its job. About 60 bucks for a new oem one from eeuroparts.