I am no specialist in the vanagon syndrome but all the vanagon I own has
that problem..

as suggested the O2 sensor, the temp2 sensor, the throttle body switch all
can give the syndrome...

as for the AFM the things to do is cleaning the the carbon track, add the
capacitor or the pig tail harness. Another thing to check is the AFM
harness it self, it has to be in good condition and the cable is not too
tight...