In one of those classic "I did so many things I don't know which solved the problem" situations, my idle is now behaving better. Not perfectly, but better. With the 02 sensor connected, and that's key.

The last two things I tried were
Fiddling with the mixture screw on the AFM while adjusting idle speed
Put an extra ground on the ECU.

I do seem to have induced a bit of lag in the acceleration when cold, so I'll be trying to tune that out next. But at some engine temps the idle is dead smooth.

My advice for those with similar problems? I have none, other than to say persevere. Screw around long enough and you're bound to make it better or worse, and then you have a baseline.

Bob W.
'87 Westy