The brakes surge with more power when the brake petal is held at a constant pressure. My guess it has to do with the brake booster. But normally a failing booster would result in less braking ability not more.

 

When you say the brakes surge with more power what exactly do you mean. On my truck when I am sitting at a light and my air cond compressor cycles the idle speed increases and I feel a surge
in my brakes based on the increase in idle speed. By that I mean I can feel the truck wanting to move forward and the brake pressure does increase.

 

It is like pushing on the brake pedal real hard but I'm not. It throws everyone in the car forward.