Originally Posted by Mister Two

You are not supposed to have the boost gauge plumbed in between the throttle body and turbo.

it matters not, both areas see virtually the same boost/vac

It needs to be plumbed into the intake manifold. - yes or before the TB, either is fine

There should be no vacuum between the throttle plate and turbo. As under idle air enters the intake manifold through the idle control valve.
no, air enters thru the TB/turbo as well - the idle cv supplements this to control idle

When you get off the throttle. the throttle snaps shut and the slight millisecond delay of the BOV opening combined with the inertia of the air still flowing toward throttle body will cause pressure between the throttle body and turbo to rise sharply then drop as the BOV opens fully.

the boost rising to 0.4 and then back down to 0.15 bar under full throttle is unusual though. You probably have a boost leak.


Really though, you should plumb the vacuum line of the gauge to the intake manifold then report back.