Chuck,
Mine has been doing the same thing for about a year now, and I have done
all the same things that you have done, except I have replaced the AFM,
also.
It had some visible cracks on the tracks, and replacing it helped a
little.
I have found that when checking continuity, on the throttle positioning
switch, that it is DOA.
I checked it in every conceivable position, and adjustment point.
It just won't let any juice pass through it.
This is (I am almost positive) the problem.
Check continuity through the TPS and see what's up.
I also find that mine gives me the most problems when it is just coming
off the cold start circuit, when the temp needle is just starts to move
above the cold temp line.
After it gets warm it is tolerable, but still not as responsive as when
it is dead cold.
A switch replacement is my next priority.
What next? :>)

Later,

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Terry 85 GL