1988 F250 Lariat 7.3 L Diesel International

Starts fine, runs ok, however when releasing the accelerator pedal the engine will stall. I have thought of as being the Idle Air control valve, though has a strange looking valve.

There is also two vacuum lines that go to a two metal tubes one large and one small, I haven't found a diagram that will tell me if the loose small one goes to the IAC