Brake Pedal Goes to Floor When Car is Running

I don't think the booster could make the pedal go to the floor unless there was either a bad MC piston seal or air in the lines. You should be able to do manually (engine off) whatever the booster does, maybe by pressing hard with both feet. There is a direct mechanical connection between the pedal and the MC thru the booster, if everything is assembled correctly. The vacuum just assists your movement.