1992 Grand Caravan 3.3 High Idle Diagnostics help

Hello, On my 92 Grand Caravan 3.3 I have a high idle problem that consistently trips the Code 25 (IAC circuitry). Here is what I have
checked and replaced. Idle Air Conntrol Motor No known vacuum leaks or other gasket leaks No other codes found The code 25 immediately sets itself even after I disconnect the battery for an extended period. I even disconnected the PCM and reconnected. It will show the code before I ever start the vehicle again. It must set itself when key is in on position and checks voltage. When I start the vehicle and backprobe the IAC connector(4 wires) with a voltmeter I believe I should get a 'cycling voltage' from under 1 volt to > 12 volts on each wire. I get these voltages on all the wires except the black/yellow one. I traced the wire back through the harness and to the PCM and everything looks OK. Resistance tests appear normal. For those who know a ton more than me: What would be your next steps if you were in my shoes? Thanks
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Toyota MDT in MO
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