... a leaking IP shut-off diaphragm. Additionally I recommend that you also purchase a couple of in-line fuel filters and:
(1) Mount one in the engine compartment where it is readily visible... in the vacuum line that runs from the IP shut-off valve to through the firewall, and
(2) Mount the other under the dash on the intake of the vent line to prevent dust/dirt/crud from entering the vacuum system.

Sam