I'm having the same trouble with my sons car at the moment. I believe the reason is bad vacuum lines. I found 4 out of 5 that had rubbed against the exhaust and burned through. I'm having a hell of a time trying to figure which one went where. There are 5 steel lines that run down the wheel well just below the master cylinder. Where they end there is rubber hoses that connect to more steel lines. That's where they burned through. If any one has any ideas on how to figure where these 5 lines go I'm all ears.