If unplugging the O2 sensor helps, then it is either suspect or you have a
different problem (that sounds stupid, doesn't it?).  If the O2 sensor is
working (it probably is, given your symptoms) then your best bet is either a
leaky exhaust or a misfire (like a fouled plug).  The O2 sensor measures
unburned
oxygen in your exhaust.  If it sees some (O2 sensor voltage < .45v) then the
computer will attempt to enrich the mixture to compensate.  If all is perfect,
then this richer mixture will burn up all the oxygen and the computer will
start leaning it.  It is supposed to cycle this way.

If any extra O2 gets into the exhaust, the computer will richen the
mixture. If
the extra O2 is not from combustion remains, this will not help.  If you
have a
leak in the exhaust before the sensor, air (20% O2) will be drawn in and mess
up the sensor reading.  If you have a fouled plug or other reason for a
miss, then
the failure to burn the O2 in the original intake charge will show up at the
sensor.  The computer's solution of enriching the mixture won't help in either
case.

If there is a hole in the exhaust, fix this first.  Do a compression check and
a general tune-up (check plugs, wires and coil, check timing).

The O2 sensor wire may also be grounded, and this will make the computer think
the mixture is too lean.

O2 sensors are fairly generic, except the electrical connector.  You can get
a Ford Mustang sensor at any auto parts place for about $40 and splice in your
connector.  Get the type with 3 wires, one black and two white (there are
one, two
and a different three wire version).  If you can wait a while, the Bus
Depot has
them.  If you don't feel comfortable splicing the wires, you will have to pay
big bucks for the "proper" one.

Malcolm H.

At 02:08 PM 9/26/98 , Dana E Hager wrote:
>After a very long conversation with three (idiots) VW dealers in my area
>who tried to tell me I didn't know what I was talking about when I told
>them that the sensor screws into the thermostat housing, I finally got
>the part. I replaced the temp sensor and still had the problem ($40.00
>if you by it at VW). If I unplug the O2 sensor it runs much better w/ a
>good idle and it no longer blows black soot out of the exhaust ( you
>need to hold a paper towel to the tail pipe to really notice it). Is
>there another test (voltage, ohms) to check the O2 sensor without using
>the CO test equipment in the bently manual.
>
>The new O2 sensor would be $180.00 from VW or is there another company
>who offers this at a better price.
>
>Thanks for all the help,
>
>Dana E Hager
>Nazareth, PA
>
>PS: Where did you find it for $15.00 ?
>