Vacuum check valve?

The check valve is most likely near the heater and AC lines. It often has three ports, one to the intake manifold, one to a holding tank and one through the firewall to the dash control head. If they fail a generic check valve can be installed. All the McParts stores have the generic check valves in the HELP brand… Look here at vacuum components… http://www.dormanproducts.com/catalog/motormite/159-164_U-W_Part1.pdf for the after market part which is somewhat similar to the OE part.