OBDâ??II is still down, but the newer problem turned out to be a bad spark plug wire. A set of new wires, and my car is now running as well as it ever had. New bit of light and knowledge, from one of my new friends here in Sacramento:  Look for white spots inside the spark plug wire. Those are a sure sign of arcing.
  And something very odd.  While I was still stumped by this problem, I did find that using high-octane gasoline seemed to help considerably. But if the problem was a weak spark, then it now seems obvious that high-octane gasoline ought to have aggravated the problem, since high-octane gasoline is more difficult to ignite. The problem also became more severe with higher temperatures (both engine temperature and outside air temperature); again, I would expect that higher temperature would make the fuel easier to ignite, and therefore reduce the problem. No matter; that problem is solved. I'm just a bit mystified by these apparent contradictions.
  So, anyone got any ideas about
this set of problems?
