My bov is staying open a small amount at idle (~22 in mercury). Its vaccuum source is the intake manifold.

When the throttle plate is slightly open the bov closes. The bov isn't supposed to stay open at idle is it? It's a blitz bov.

 

no it shouldnt stay open. have you tried tightening the top bolt down?

 

ok...i have had a few problems like this and i have the blitz also. you have to take it off and apart. when it's off, take the horn off. then you will have to compress the c-clip with needle nose and the piston will spring out (take note of assembly order). you may find the pressure port has been scarring the piston...mine was. go ahead and clean the dirt out of the chamber and off the piston. champher the piston side of the port where it is sharp (obvious where). slightly oil the piston. i used mobil. without the spring, put the piston in the chamber and make sure it slides without any binds. with it in the chamber you can get it out by blowing in the vaccum port. reassemble in the same manner as you took apart. seal to charge pipe with a gasket or silicone.

 

Also check the vacumm line that goes to the blow off valve. It might be clogged.