I have a brake pedal that can be pumped up with engine stopped, if you start engine the brake pedal will go almost to the floor. I just replaced the rear calipers with new pads. Then this problem started, so I replaced the master cylinder. Did not help, could it be the power brake booster? Good vacuum to booster.
Just to add to this one since you have rear calipers you have abs brakes and you said the problem started after replacing the calipers. My question is how did you bleed the brakes?Abs on that car has a special bleed procedure.