Brake booster check

[micbrody]

On my quest to improve starting and running of car, I went to test the vacuum seal of brake booster, since if there was a big leak, I would expect it to alter idle; maybe starting issues. I put mityvac on disconnected end (manifold side) of booster hose . I was first able to get a vacuum of 15-20, but then it went to zero. I tried again; but as pressure went to negative 5-10, it would suddenly release. I fully disconnected hose. It has no leaks. The check valve works. However, again, the booster seems to only hold a 5-10 vacuum. I was curious if booster was working at all. I drove it without it connected. very difficult to to brake. When reconnected, brakes work very well.
So my interpretation: I have small leak in brake booster diaphragm. Not enought (yet) to dramatically affect booster function; but enough where my idle slightly varies, probably every time the booster diaphragm's tiny leak looses vacuum. Am I correct?
Or is my mityvac brake booster vacuum test flawed, in that booster is suppose to lose vacuum???

[DieselSpider]

In general the booster should maintain vacuum to assist stopping the car after the engine has stalled. Most will maintain boost for a few applications of the brake pedal after the engine has been turned off even after 24 hours or so.

[micbrody]

So does my test procedure with mityvac confirm a small, abnormal leak?

[DieselSpider]

So does my test procedure with mityvac confirm a small, abnormal leak?

It would appear too unless the MityVac itself has a leak. If you plug the line does it hold vacuum by itself. You have to test the tester and verify it holds before you can do a proper leak test.