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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