Posting back with the happy news that the idle surging/hunting that drove me nuts for a month is gone.

The bottom line for those who try to solve an idling or related problem: If everything you do under the hood seems to make no difference, don't declare defeat. After you've done your thing, remove (and clean) the battery cables, then put them back on. That's how my fix kicked in.

Wiser heads here might know better, but it seems to me that interrupting the power reset the ecu, prompting it to recognize whatever I had done to fix the surge earlier. As soon as the cables were back on, the idle returned to normal and the engine light went off for the first time in a long time. And after 3 days of stop and start highway driving, it's still working fine.

Another lesson: The limp-home test is not a surefire way to test the amm. When I disconnected it, the surging stopped, and so I was about to order an amm, when someone here told me it could still be good. And so it is. This is the second time I almost shelled out needlessly for an amm.

I don't know which of the following steps took care of the underlying problem but here they are, offered with thanks to those who guided me:

-Replaced air filter
-Cleaned gunk out of the amm with the proper spray cleaner
-Plugged a hole in (then replaced)intake hose
-replaced clogged flame trap and associated hoses
-cleaned crap out of throttle body (without removing it)
-removed and cleaned idle air control
-pulled vacuum hose on fuel pressure regulator and made sure gas wasn't getting into it
-stared at mysterious things
-read FAQ to the max
-cursed
-prayed
-tried a few minor things I've forgotten
-gave in to despondency over how nothing I had done solved my problem
-vaguely remembered something I had read deep in the archives, and disconnected the cables, cleaned connections. and, poof, success.

until, you know, something else happens......