I have a 1984 Vanagon Waterboxer that seems to be eating catalytic
converters in less than a year.  I have been told several different stories
about what could be the problem.  Injector pattern not right, wrong mix,
air-fuel ratio wrong, etc but most of this should manifest itself in some
other symptom.  The latest from a mechanic is that I should be using premium
gas in the van (octane 92) rather than octane 87.  I am just at a loss right
now.  The van gets 20MPG which includes some distance going up a 6 degree
grade with the air conditioning on and the still being able to acclerate on
the freeway going 70 MPH.  The 1900 engine has been replaced with a 2100
(two years and many miles ago).  I am looking for inputs as to what could be
the real problem.  Also, at idle, the engine seeks a lot of the time.  By
that I mean it revs up a little and then settles back down to normal.

William