Mention this to list with trepidation because it usually ignites flame war, but IMHO is important:
At same time JZD was messing around with idle speed motors, Volvo just used brass screws already built into PRV to set idle. Low tech, yes, but less subject to problems. I think every owner should know how to use in case automatic idle system fails or needs diagnosis, if nothing else. Simply advising "just snug down and never worry about them again" deprives owners of a valuable feature ALREADY IN PLACE (no mods necessary).
FWIW: is the ONLY idle system on #5939, and you saw first hand how well it works.
Side note: you've got ignition "advanced" and "retarded" flipped: advanced is early, retarded is late. Might confuse someone's advice if they didn't listen carefully to full explanation.
Bill Robertson #5939