Ok, so poking around at the intake some more. Based on the appearance in this photo, is the bi-metal switch missing?
Also, not sure what the name of this is, but I know it should divert the intake flow to pull in air heated by the exhaust manifold while the bi-metal switch applies vacuum:
I found that it doesn't work even with vacuum applied, and doesn't seem to be leaking any vacuum. Is any of this worth replacing, supposing the parts can be located? Or am I just as well off just capping off the vacuum line and removing the ducting to pull from the manifold?