When I had the old (210,000 mile) 1.9, in my '85, it would run smooth
and feel normal with the O2 sensor disconnected but it got terrible gas
mileage.

When I put the rebuilt 2.1 in (using a rebuilt 2.1 AFM and a 2.1
throttle body), I left the O2 sensor disconnected (using a stock 1.9
ECU) expecting lousy mileage.  However, driving a max of 51 mph, I
averaged 24.92 mpg over a 1200 mile distance.  It ran super well with no
hesitation and no flat spots.

After arriving in Virginia, I swapped in a Euro 2.1 "Digijet" ECU
(performance ECU for 1.9s) which doesn't accept an O2 sensor input
anyway, and drove back to Maine doing about 63 mph and using the air
conditioner most of the time.  I averaged 22 mpg during the trip home.

The only times, with any of my three running Vanagons, that I have
experienced poor performance attributed to the O2 sensors, is when a bad
one was hooked up.  Disconnecting a bad O2 sensor always allowed the
engine to "Act" normal again.

Kudos to Boston Bob!!  I'm in love with the new engine.

Mike
Houlton, Maine