GoWesty emailed back and declined to share their information, citing "that
data is proprietary".  It really isn't, just as knowing the expected output
voltage range of a healthy voltage regulator isn't proprietary.  Oh, well,
it was worth a try...it just means a little more work on our part.

So, here's what we need to know:
* The PWM duty cycle being feed to the idle air valve when:
     --the engine is cold, the starter is engaged, and the coil is shorted
     --the engine is cold & running
     --the engine is fully warm & running
     --the engine is fully warm & running with PS operating
     --the engine is fully warm & running with AC on
     --the engine is fully warm & running with PS operating and AC on
*  The current draw from the idle air valve at a known duty cycle.(or feed
it straight 12v and measure the current draw.)
* The base voltage and the peak voltage coming from the Hall sensor
The above items will need to be done by someone with a scope and a healthy
ICU & idle air valve(and PS & AC).

*  Which connector, 4/ST2 or 11/ST1, supplies the PWM power to the idle air
valve. (and confirm that whichever supplies the PWM power, that the other
is a ground connection.)
*  What is the voltage at the coolant temperature sensor when cold and when
160 F.

I think that this would provide all the information needed to design the
circuitry and program the microcontroller to drive the idle air valve.

And once a prototype is built, we will need a vict-- I mean volunteer-- to
connect it to their rig for testing & fine tuning.  Preferably in the
Portland, OR area.

--
Brett in Portland, OR
"Albert" '82 VanFox I4 Riviera