Well, I have never seen a car with one of those valves. It appears from the parts film to be a decel valve. It is teed into the inlet and outlet hose of the aux air valve with a vacuum line going to a third port. Based solely on the place of installation I would say that it is intended to add air on decel either for emissions or idle stabilization.

I don't suppose it should rattle, but if you plugged all three ports it would work like most 110 engines worked and eliminate any problem that you think it might cause.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician