I noticed today that the top port of my wastegate was pulling vacuum. We broke my throttle body gasket while changing out the TPS sensors and had low vacuum at idle (~10 inches Hg) so i assumed that's where the problem was. Changed the gasket today and it was still low, so i traced it back to the top port on the wastegate. I have it setup to run off the wastegate, so the top port is vented to the atmosphere and the side port is tapped to the intake manifold. At idle when i plug the top port, vacuum goes back to a normal 20 inches Hg. For reference i'm using a Tial 40mm wastegate. Car runs fine, wastegate holds boost where i have it set, and we dynoed it exactly like this. So it's not big a problem, just can't figure out why it started doing this.

 

maybe there is a small rip in the diaphragm