I picked up another cheap accent over the weekend that I plan on turning into an auto cross car only. I'm having some issues with the brake son it. This is whats going on, When the car is off, I have to pump the breaks 2 or 3 times to get pressure. but then it keeps the pressure for a few hours. With my foot pressing down on the brake, it holds the pressure no problem.

With the car running, I again have to pump the breaks, and it looses pressure pretty fast. When I pump the breaks the engine idle fluctuates with the pressing of the pedal.

I have bled the breaks, and flushed the fluid using a pressure bleeder. Ive also swapped out the Master Cyl. Im at a loss now. Other then changing the booster, I dont know where to look next.

 

I was thinking the booster, and that idle may fluctuate because you have a vacuum leak when depressing the brakes.