why does my volkswagen bus stall when I push in the brake pedal?

[greenthumbed420]

I have 1978 Volkswagen Van. It is a fuel injected 2000cc engine that has been rebuilt less than 500 miles ago. Whenever I push in the brake pedal to stop it stalls. I've adjusted the idle already and that helps a little bit. The van idles fine in neutral and seems to drive fine. It's only when I apply any pressure to the brake pedal that the engine loses rpms and shutters and then stalls. Any ideas?