Ray I think you're right in part. That's to say I don't think the idle fuel mixture is the *only* issue. Shop it's been going to doesn't have a sniffer so we've never been able to set the idle mixture at the ECU. Smog shop should be of some help.
I suspect trans troubles. Need to disconnect the modulator vacuum lines at the plenum, cap them and see if the idle stabilizes. Will fiddle with the car this week, tune it good and so on.
Also need to get busy on rebuilding the harness which is pretty crispy in places. Also want to install a wide band meter which will help greatly in diagnosing as well as dialing in the MPS.