Keith,
If this is a true Vanagon Syndrome* then I would concentrate there. One easy
modification someone suggested is grounding the AFM metal body to the engine
to discharge static buildup. I do not know if it works but I added the wire,
just in case.

IMHO, the idle stabilizer only has any effect at idle.

I did not see anything on your list about the O2 sensor. Maybe you could use
one of my O2 sensor monitor gadgets? See website below.

Ken Lewis
http://neksiwel.20m.com/

* Vanagon Syndrome: Computer gets confused by erratic, noisey signal from
AFM. Usually fixed by reseting the computer, expensive VW harness mod or
small filter capacitor added to AFM.