probably a vacuum leak. Check to see if the hose connecting to the vacuum tank on the firewall came off. On my car the vac tank is to the left of the washer pump. The hose connects on the bottom . There may even be a plastic valve connected to the hose like on mine.
You might also have a bad vacuum diaphram or loose hose under the dashboard. That would require removing the lower black dash trim panels and listening for a loud SSSSSSssss noise.
Good Luck
========= Harryface =========
1991 Pontiac Bonneville LE 3800 V6 ( C ), Black/Slate Grey _~_~_~299, 999 miles_~_~_
~_~_~_~_U.S.A._~_~_~_~_~_
~~~The Former Fleet ~~~
89 Cavalier Z 24 convertible
78 Holiday 88 coupe
68 LeSabre convertible
73 Impala sedan