Many ECM parts are 5V including TPS but I think IAC is 12V.
ECM scanner can see ECM is sending X but ECM hardware says not happening.
One Typical fail is 87-88 Duke ECM not turn on injection because Driver(s) on the ECM board have problems.
Just 1 crack solder joint is all it takes to "Kill" a ECM.
All four IAC lines are driven by one 12V chip and maybe is "dead" for same reason or dead outright.
Meter or generic light might help or not because IAC is a Stepper motor and maybe one or both coils are off when tested. Worse is likely easy to fry the chip if you short the lines. For this reasons... Can get a Noid light for IAC sim to injector Noids but have 2 lights to check each coil feed.
88 TBI is 700 type and noids will match the connectors for each part so doesn't damage them.
IAC reset is drive over 35mph
or car parked and throttle above 2000rpm for some seconds when ECM is scanned. Watch IAC/idle reset yes/no when you push the gas.
When you get another ECM save the PROM and move it to new one.
See my Cave,
ECM Heat (and rest of section) because Heat doesn't help either even when ECM is replace.
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave