Vacuum valve from EGR?

My 100K mile 1977 280C passed all but one portion of the rigorous smog test here in California. The measured emmissions were WELL below the allowable levels, impressive for a car of this vintage, and with so many miles on it. The one place it failed was that there was no vacuum at a valve near the front of the engine compartment (on the driver's side) which I believe is connected to the EGR valve. With no shop manual it's hard for me to know how they're supposed to work. I'm wondering if the EGR itself is merely clogged, or if something connected to it is inoperative. Can anyone point me in the right direction so that I can get this magnificent beast back on to the road where she belongs?