I have to disagree with some of the posts on this.
Most every vacuum operated power brake system introduces a bit of extra air into the intake system intermittently when the pedal is pressed or released.
Here's how to tell normal from not normal.
Any of us with power brakes can press and release the brake pedal and get a change in idle speed or a light miss for a second.
If you press the brakes and have a continuous miss when holding the pedal down, chances are the diaphragm has some sort of leak.
If you press the pedal and release it and have a miss for a second and then it recovers, this is normal.
Anyone one of us with vacuum power brakes can prove this by idling your engine and pump the brakes a couple of times and notice the idle either increases a little momentarily, or there is a miss for a second but it recovers right away.
Just because there is a miss when doing some operation of the brakes does not prove the booster is bad.
This has to be diagnosed by when and for how long the idle changes, the miss occurs or a vacuum leak down test is done on the booster.
