[Linked Image from i.imgur.com]

I used the bad-manually-extended ISC in the throttle body and connected the new-good one to the harness hanging outside. I could feel the stepper motor vibrating in response to RPM changes, but the pintle moved no more than 1/16" up and down.

For the meantime, I am running the harness unplugged with the closed-off/extended ISC, until I get my hands on a known-good ECU to test.

1989 Dodge Raider 3.0L V6
1987 Suzuki Samurai 1.6L 16v