I don't see an '89 driveability PDF there now.
However, I've been trying to trace the problem today, and discovered while switching out the ECUs that if I wiggle the wires a bit that are coming out of the middle connector of the ECU, I can cause a stall or recover from a stall when it starts. I'm not wrenching on them, just poking them a bit to move them. Seems especially to be the blue/Green wire in the corner of the connector. I don't know if this would indicate that the wire has a short in it or if the wire is not making a good connection in the connector, or if the connector is letting current across wires and causing issues, or what. And it may or may not explain why the newer ECU is idling high and loping.

So that's where I am at right now. Not sure how to check the connector. The wiring harness is pretty tight up in there under glove box. Don't know if I should cut the ECU connector out and splice in some longer wires or what. Any opinions?

Thanks.