Sounds like an iacv issue then. The iacv plug goes through a mini harness that runs across the intake manifold then plugs in at the dual gray plugs above your TB. Id grab an FSM and validate what wires they are then do a continuity check with a digital multimeter set to resistance. Make sure the wires arent broken or shorted to ground on the mini harness. Check your connector on the engine harness side and make sure it isnt all crapped up.
No change when plugged in or unplugged but change when you restrict air in to iacv tells me either the iacv is stuck, or the computer is not able to change the valve position. Ill be stuck at home all weekend after i pick my car up tomorrow so ill dig through the fsm and see if there is a fuse or anything else that might have failed.
https://www.nicoclub.com/service-man...sx/1996/ec.pdf
Ec-222 and 223 have your harness and miniharness pinouts
10A fuse #23 on the left column of your fuse box by your left foot