I'll second the idea of a major vacuum leak. The leak may not be just in your headlight vacuum system though. I've seen a loose PCV grommet kill an engine once. Also, the biggest vacuum draw other than the PCV system is the power brakes. I'm sure that when you are putting your car into gear you're holding the brakes first, eh? Either a bad vacuum hose, bad check valve, cracked vacuum Tee on the firewall or maybe the booster took a dump. In all reality, this problem of yours should be relatively easy to track down. Keep us apprised!