I know this subject has been posted to death, but here goes. Just rebuit all 4 calipers with new seals and boots, installed new master cylinder. I used power bleeder and tried for half a day to get air out of system. Brake light is on, of course, and pedal goes to floor. I also tried the old fashioned way with 2 people, one pumping pedal, to no avail. When someone pushes on pedal and I open front bleeders, they say the pedal moves down faster, but not when I open rear bleeders. I guess porportional valve is partially blocking rear system. I have been bleeding brakes for 30 years and never had such a problem with a system. No leaks anywhere. would a bad proportional valve hold trapped air?, or should I just keep trying to bleed them? I have tapped on calipers while bleeding, raised one end of car, tried all the tricks I know of to no avail. By the way, I just bought the car a few months ago, and it has been sitting for 14 months. The brakes were very soft when I brought the car home.