Ok a little more data - the G102 ground was a little bit lazy on the voltage drop test compared to a ground wire to the battery, cleaned it up and it was good after that.
Engine did run better as long as I didn't touch anything, when I shake the ECU pigtails it went bad though.
Substituted a backprobe ground from ECU pins C2 and C3 to ground and things improved, now the only symptom is idle control when I move the wires with engine running, I'll continue chasing that down...BUT in looking through the ground distribution from the schematic I see it lists a G103 generator bracket ground.
My harness doesn't have that, or any hint that it ever had one there. So, quando quando?
Schematic says that's where the ECU grounds go.
I'm going to make an executive decision here and relocate my ECU grounds so I know where they are at least. Maybe that will sort out the IAC issue too, but I'll treat it as it's own issue if not.