I would not think so. It's possible of course, but you almost always feel air in the system as a very mushy pedal. Not "soft" per sé and usually not just for the first bit of travel, but overall mushy.
It's possible that some of your bell-crank linkage for the booster is having an issue.
Or the pedal rod might be coming loose? I would certainly visually inspect all the linkage if you have not already.
It's possible too, that there is a bit too much gap between the booster rod and the back of the master cylinder. This would not only feel "soft" to the foot, but would also not give you any braking.
And last but not least, the booster itself may be giving you some negative feedback during that first bit of pedal travel.
The brakes are still strong though, so that's a very good sign.
What happens when the engine is off and you push the pedal? Very hard right from the get-go? Or do you feel like you can push the pedal easily at first still? This is after you've pushed the pedal a couple of times to get rid of all vacuum.
Then, after the last test, push and hold the pedal while you start the engine.
Normal behavior is for it to be tight and high, then as soon as the engine starts cranking and vacuum builds up, the pedal should immediately be easier to push.
And another test would be to apply the parking brake one or two notches if you can, to see if that changes the attitude of the pedal. If yours is real tight, you won't be able to do this easily. But if you can get three to five clicks on your parking brake when setting it, then one or two clicks to test their adjustment should not cause any trouble.
Drive it with the pedal down those two clicks and see if your main brake pedal feel changes.
Let us know how that all works out.
Paul
