It's hard to get accurate measurements with a typical meter because the
voltage changes rapidly (if the sensor is working right).
An old fashioned analog meter with a needle responds faster, but uses
too much current and would wipe out the signal you're trying to measure.
With a digital meter of reasonable quality you should be able to get an
idea of what's going on:
  Connect the negative (black) meter lead to a good ground point.
 Connect the other lead to the place where the O2 sensor wire connects
to the wiring harness, with the sensor connected.  With the engine
idling, the voltage should change continually in the range between 0 and
1 volt, if the sensor and ECU system is working.  Most of the readings
will be inaccurate because the meter is not able to update fast enough
with the voltage going up and down once a second or so in a working
system.  It should go back and forth from near zero to near 1 volt; the
more times it crosses half a volt the better.
   If the voltage stays steady enough that you can get a solid reading
the sensor is probably bad.  If the voltage stays less than half a volt
the sensor is weak or the ECU and fuel system is not capable of
producing a rich mixture for some reason.  When our Golf had a bad
sensor, the voltage would stay low most of the time and then slowly move
upward once in a while and then drop down again.
  If you can search the archives for posts by Mark Keller (sp?), you may
find more useful info on this topic.

Hope this helps,
Larry A.

Jeffrey Vickers wrote:

> No. I just assumed that since I unplugged it and the stumbling went
> away that that was the problem. I have a little digital multimeter,
> though. How do I do the check?
>
> Thanks,
> Jeff
> On Apr 17, 2006, at 2:55 PM, Larry Alofs wrote:
>
>> Have you checked the sensor with a meter to be sure that it is weak?
>>
>> Larry A.
>>
>>
>> Jeffrey Vickers wrote:
>>
>>> I've been getting stumbling/missing between 3 and 4K rpm so I
>>> disconnected my O2 sensor and it seems to have cured the problem.
>>> What's the consensus on a new sensor? Bite the bullet and go with and
>>> OEM unit or get the generic and splice in the plug?
>>>
>>> Jeff
>>> 87 Syncro Westy
>>>
>>
>>
>