I had that problem... Turned out that the main vacuum supply line had been severed in the engine bay.

If I remember correctly, one end of the line terminates inside the car in the passenger footwell, over by the center console. The line becomes part of the main wiring harness, comes up under the fusebox, around the back of the firewall to the supercharger right behind the throttle body.

I can get pics later if you would like...