I too had a similiar problem with the cat conv, although it came on a little
more gradual.  I drove home approx 100 mi on the turnpike, gradually losing
power.  For the next several days I could start the van, but only drive short
distances before it would die.  After normal tune up part replacements, it
was eventually towed to the VW dealer.  They also couldn't figure it out
until they pulled the O2 sensor to check it and all of a sudden the back
pressure was relieved and it ran fine.  I was suckered into the cat at VW
prices and cannot remember if I ever found an aftermarket cat.

Kerry
stanleyk@hslc.org   '86 syncro