The rubber plenum connects the airflow meter housing to the throttle body. Taking the idle circuit air from this junction allows it to be metered. If you think about it, functionally the idle air valve bypasses around the throttle valve. You want it to serve the function of adjusting the air leakage around the throttle plate to maintain a constant idle speed - or vary it according to temperature, etc, inputs to the controlling ECU.
The airflow sensor plate will deflect in a correct metering of the idle airflow, and adjust the secondary fuel pressure for correct mixture control, both from its mechanical connection to the fuel distributor and the electrical feedback to the ECU from the sensor on the side. The ECU then fine-tunes secondary pressure via the EHA on the fuel distributor.
The plastic pcv device has only an orifice for metering. There are no moving parts, so nothing to wear out. Worst case scenario is that it would be plugged, and all crankcase vapors would pass to the intake via the air cleaner element. However, I would treat this device as fragile - as with all the plastic connectors. I carefully cut the old, hard hoses off to prevent damaging them. The new hoses are pliable and don't present a problem.
I don't know why there are three wires on your idle air valve. I know ours has only two contacts.