What is this plastic device in the middle of these images?

I ask as I was hunting down boost leaks and when evr I pressureised the system via a commpressor over about a bar it squeeled like a pig trapped in a shed with a horny farmer! Is this right? Can't say I hear it when driving but theb I don't know if I would over Exhaust and road noise etc.

 

[Rik] "It's a fish, Mike."

IIRC it's some kind of vacucm-operated valve for the emissions/oil breather system.

 

Cheers mate thought itnwas to do with oil breather set up but wasn't sure why it was screamin under pressure but if its vac operated then that explains it

 

I'd replace the whole vac hose and use new tie-wraps. The noise is bound to be air escaping when the valve is under positive pressure. Could be the valve itself of course; why not try poncing a replacement off a Subaru/breaker specialist, too?

 

PCV, Pressure control valve

 

That's it (couldn't think of its name!).

 

Will price 1 up from the stealers!

Would this cause boost issues? As in sometimes I make the boost I should and then the next time I stand on the loud pedal I don't or it pulses up and down?