Your idle speed is controlled by the ECM. The idle adjustment is intended to set what is called "minimum air", not to set the desired idle speed; you should not fool with "minimum air" to compensate for a problem in the idle circuit. The AIC (air idle control) motor, located on the throttle body, responds to ECM output. The AIC has a plunger that controls the amount of air bypassing the throttle plate. Too little air, low idle, too much air, high idle.
Your problem seems to be too little air. This indicates a bad AIC (quite possible), a plugged bypass passage in the throttle body (unlikely),a bad connector on the AIC (remove and clean contacts), or a bad ECM (not likely).
The AIC has two sets of windings; one set to retract the plunger (more air bypass, higher idle), and one set extend the plunger (less air by pass, lower idle). The ECM send pulses to the AIC to effect retract and extend. An inexpensive LED voltage tester will tell you if the ECM is talking to the AIC--back probe the connector, one set of windings at a time, while the engine is idling; you should see the light blinking rapidly. This won't guarantee the ECM is good, but I'd bet it is, as is the wiring to the ECM if you see the blinking.