the maf is on the intake side of the turbo. it does not have the charged air for the bov.

the problem is that most stock bovs are actually bypass valves which are supposed to vent back to the intake. they are slightly open during idle. (i've seen this with dsm, bosch, and volvos i've tried) most aftermarket "blowoff" valves are made to vent into the atmosphere and stay shut during idle.