I see a fair number of members have read this but no one seems to have any ideas.
For the benefit of anyone that may be having the same issue, I'll post what I have done to correct this issue.
I have lost count of the number of times I have taken the air intake stuff apart and put it back together, cleaning this part and then that part each time. Some I have cleaned more than once, as it seems difficult to get all the gunk out with any one try. Last night I did a fairly thorough cleaning of the whole thing, air tube, sensors, switch, and throttle body. After all that cleaning, it still was idling a little high every few seconds on the driveway, but not as high as before. Today I took it for a 60 mile drive, both highway and city streets, without any sign of the idle problem. All seems good for now.
It's hard to tell what was causing the idle issue, but the lesson I have learned is that if you come across the same problem, just clean, clean, clean everything and anything that affects the air flow on its way to mixing with the gasoline. After years of dirt and carbon accumulation, that contamination starts to take its toll.
Good luck.