I see, what kind of vac reading are you seeing? Ive been told that the symptoms of a bad booster is vac decreasing sharply with your foot on the brakes and not recovering while holding them down. I had one once that if I pumped the brakes on and off at idle, it would allmost stall out the car. The best test ive heard of is to shut off the car then pull the valve out of the booster and see if it has vac inside (hiss). Although I would expect it to go away after 15 minutes or so. You could just plug the vac line for one short test run and see if your symptoms or guage reading changes, just dont tailgate