I would like to express my thanks to all of you who helped me solve the problem.
Also, please do not feel slighted if your name is not mentioned, as I can not recall everyone.

I have just completed a 3600 km(2250 mi) trip through beautiful but very mountainous British Columbia. The 85 
Vanagon ran flawlessly for the whole trip and the gas mileage was a respectable 24 miles/Imp.gal.(19.2 mi/US gal).
The van was fully loaded with 4 people, camping gear plus an additional box attached to a rear rack.

I did 4 things that may have solved the problem:

Cleaned the contacts of the AFM meter.  The meter seems to have a crack in the circuitboard just at the
 very beginning.  As a result the resistance goes to maximum almost immediately and stays that way for the 
rest of the swing of the contact.  I was going to replace the meter before going on the trip but ran out of time.
I did put in the capacitor modification before I left though. Cleaned the contacts with a good contact cleaner.
This probably solved the bucking problem.
Should I replace the AFM as for city driving it runs to lean and may cause some damage?

Replaced the ignition cylinder and switch as there was some play.  Rattling the keys while driving caused the
engine to quit.  This may have really solved the intermittent stalling problem.

Replaced the oxygen sensor as I was replacing the collector pipe anyway.  I don't know if that had anything
to do with the bucking or stalling.

Put a bottle of injector cleaner (Chevron brand containing Techron) in the gas tank.

That's it.  Runs great.  This is the love phase of my love-hate relationship with the van.

Thanks again to all of you who helped.  

Alfred

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