Good news - I passed Test Number 4! NOx at 15 & 25 MPH went from 1497 to
1074 and from 1090 to 326. The CO & HC numbers went slightly up and are
now "average".

I spent a day checking everything and found two likely causes: The first
was a split connector on the aux. air regulator intake hose. The other was
an exhaust leak right at the flange where the two exhaust header pipes
combine into one. This was about 4" from the O2 sensor and was most likely
throwing it off. I installed a new O2 sensor. The old, (almost new) one
read from 0.48 to 0.52 V so it was probably OK. The new one read a steady
0.55 V after the fixes. I installed some rebuilt injectors for good
measure. I didn't change the catalytic converter, but it is still suspect -
 I just squeaked by with my 15 mph NOx number. Maybe next year. For the
record, it was made by Magnaflow.

Thanks to all who answered - you gave me plenty of ideas and I learned
lots in the process. I am still kind of amazed that 2 local VW mechanics
didn't have the gumption to check for something as simple as intake &
exhaust leaks first. The $320 they cost me sure was a waste of time and
money!

Walter
85 Vanagon 1.9L