I've changed the front and back brake pads, flushed the brake system with new fluid, and bled the brakes. The pedal is nice and stiff until I start the car, then it goes to the floor. I changed the master cylinder and bled it per the instructions that came with it, re-bled all the brakes, and still have the same problem. I've also used my Autel 808 to bleed the anti-lock system. There are no leaks in the system. I've changed the brakes and fluid in this car many times, without any problems. Any help will be greatly appreciated.
Jack

Was it doing this before you touched it or is this something that cropped up afterward?

Atterwards.

If you keep pushing the brake pedal while the engine is not running, does the pedal eventually go to the floor?

No, it'* very stiff, it only goes to the floor when I start the car. Just to be clear, after starting the car the pedal is very spongy on the way down, it doesn't just drop to the floor. I took the master cylinder off and re-bled it to make sure I got all the air out, then I re-bled the brakes and got the same result. I jacked the front end of the car up to see if that would allow the air to move to the front brakes, It has sat all night, and I haven't touched it yet today to see it that helped. Thanks you your help.
Jack

This is a weird one, so I just want to make sure I'm being clear: As it sits right now, after having sat overnight, if you don't start it and then push on the brake pedal firmly for at least three minutes, it does not go down at all?

Yes, it'* as stiff as a board. I have bled the back brakes twice today using the air hose and bottle method, and then by pumping the brakes. The pedal seems to be a little bit better, not going as far down. I have a hard time believing there is that much air in those small lines. I also bled the anti-lock system again. Going to do all four later today and see what happens. Thanks again for your help.

Bench bleed the master again and tap on it while under pressure to get trapped air out.

I did, then I re-bled all the brakes by the air (vacuum) method, then pedal bleeding. Same result. Bummer. One odd thing, when using the vacuum method the air bubbles never stop, but when I bleed them via the pedal method, I don't get any air at all. Strange. I have a reverse bleeder coming, we'll see how that works. Thanks.

Put thew master in the vise. Bleed it and terminate the ports Will it hold? If not the master is bad.