Issues fixed. Had multiple things going on. Distributor vacuum canister leaked. Replaced with the 123 distributor.

Tiny vacuum leak ended up being a worn throttle body linkage shaft (at least that’s what I’m calling it). Was a very minor leak, but a leak just the same. It didn’t show up on the smoke test I did, but it did show up when I tried pressurizing the system. Replaced with a NOS throtyle body I found on ebay (got lucky there, price was reasonable, too). It doesn’t have the safety spring like the later models, but I doubled up on the TB return spring for piece of mind.

Engidlebidles at a perfect 950rpm.

Next step was to tune the air fuel mixture. The rebuilt MPS I got from Jeff had been reset to factory default settings, but was way too lean for my car as I had originally thought. I adjusted the MPS using Chris/Tangerine Racing MPS adjustment tools in conjunction with the Plex wideband sensor I installed last year.
My AFR is now 13.5 at partial load, and 12.5 at WOT. Idle is at 12.2. I may try bringing the idle mixture up a bit with the ECU knob.

The car drives fantastic. Having a steady idle after 12+ years of ownership is a thing of beauty. And just in time to enter the car into the Edmonds car show in Sept 8th!

What a journey! Although extremely frustrating at times, I sure learned a lot through the process.

Thanks for all the input/help from everyone!