You more than likely have a vacuum leak. Nose around under the hood and look for one of those lines from the brake booster area toward the engine being disconnected. Also, look for cracked/busted vacuum line connectors. If you do not find any vacuum leaks then it could be in the vacuum pump shutoff mechanism but most of the time it is leaking vacuum hoses. I would recommend you get a manual and a vauum pump and do proper troubleshooting of the vacuum lines.

__________________
Jim