Brake booster problems?

[Money pit Beretta]

I have owned a few cars in my day, but have never had a brake booster problem. I may have one now. At idle in park or drive if I pump the brakes more than two times quickly the idle will go up. When I do that in gear the idle will hit around 1,500rpm and then drop with a half stall. Then the engine will idle up and down then smooth out.

My vacuum checks have shown a small leak on the main line to the HVAC. That goes away if I use the HVAC system in any way(if it is warm out that is). I will be getting some clamps to seal off those leaks. Today I plugged the barb at the upper intake and nothing changed on the brakes. I thought that the HVAC system was leaking too much and adding air to the intake. Really that was a long shot and I'm just will to try anything. Then the check valve on the booster was swapped with a "help" one I found at the JY. There was no change when I pumped the brakes. There was some vacuum in the booster when the "help" check valve was pulled out.

How do the brakes work/feel? There is the normal pedal drop and the they grab. The braking force feels normal, but then seems to fade a little when pushing the pedal down to stop the car. You can pump up the pedal with the engine off or on. Holding the pedal after it is pumped up with the engine on will make the pedal sink.
I do think that the brakes could be bled, but this vacuum problem must come first. The rotors are now warped do to this and bleeding can come after they are turned or replaced. Also if it is the booster I have a master just waiting to go on(more bleading).

One last thing: the upper and lower gaskets have been replaced. I replaced the upper last week just incase there was a small tear in the gasket like last time(there wasn't). Found the TB bolts to be loose and retorqued them. I may put some gasket maker on the gasket to seal it(it has been opened up by Ben to the 65mm size and I'd like to keep it).

[woody90gtz]

When my booster went bad I could definitely hear the hiss and watch the rpms jump a couple hundred. Brakes still felt fine though. Holding the pedal did not drop it.

[Hawk2010]

If the brake pedal is sinking to floor when holding it down then you have either air in the line or the brake fluid could be bypassing piston in master cylinder and going into booster. Pushing peddle a couple times quickly would cause engine rpm to change. I've seen bottom of booster rust out. When I took it apart it had brake fluid in it.

[Money pit Beretta]

Thanks for the support Woody and Hawk. The plan now is to start looking for a good quality booster. Once that is found, it and the master will go on along with anything else that is needed. Looks to be a brake system restore, less the lines(but we will see on that).