This is an inline VW motor but running all the electronics, same as and
probably directly from, a Digifant Vanagon...started with an 84 van...now
has a 92  Jetta 1.8 liter 8 valve motor in that van with the diesel motor
mounts but it is a gas motor..

   I am almost sure I have the problem isolated to the 02 sensor..The
engine runs OK with that disconnected, plug it back in and after a few
seconds, the engine goes full rich and smells like unburned fuel from the
exhaust.

   Just about a week ago I replaced the old O2 sensor with a new Denso one
and it ran perfectly for about 500 miles of highway driving, until
yesterday when it began stumbling and losing power.   If I switched off and
back on (ignition) it cleared up for a few seconds...so I made it home that
way and I have been working on finding the cause.  I have had some great
help so far, but I am still not sure exactly where the problem is...The
wires leading to and from the old O2 sensor were brittle and cracked.   I
spliced in the new one, but the harness from the plug to the ECU, that also
had some insulation cracking and brittle wires...Those I have also patched
up for now, I will try to find another 'pig tail' to replace that later,
but for now I am trying just to isolate the problem so I can get the proper
fix done.

   Now here is where I am in this process...I have the O2 sensor out again,
on my bench.   I have access to the plug back into the harness.

   I want to bench test the 02 sensor, which I am told can sometimes be bad
even though it is almost new...I am told there is a way to put a propane
torch on it and get a reading from my voltmeter, but could someone outline
this test procedure so an electrical dunce can do it?

    I am also told I should have continuity between the signal wire and the
ground wire from the ECU harness....I don't see that, ignition on or
off...When I put my voltmeter probes on the plug back to the ECU, the one
that accepts the plug from the O2 sensor, and I turn the ohm meter to the
20k scale, I see no movement at all from the digital readout....When I
probe the two heater terminals, I do see continuity...

   Where the signal and ground wire enters that shielded casing, there was
some frayed wires that could have been contacting the metalic shielding...I
trimmed that back a bit till I have clean wires and I have repaired the
fraying.   So should I have continuity between the two terminals there at
the O2 plug back to the ECU, or am I totally off base here?

   OK another thing I changed was my Temp II sender....I have not tried
adding that into the diagnostic process yet...Should I?   I have been
assuming that since the engine runs clean with the O2 sensor unplugged, or
after I cycle the ignition off, that the problem must be in the O2 sensor
circuit...Should I put the O2 sensor back in and try un plugging the temp 2
sender?...I have some spares that I can substitute also...

   Any advice would be greatly appreciated... and thanks in advance

  Don Hanson