I started earlier to write a test but I had to verify which connectors your car would have. It turns out that your car should be early enough to have the diagnostic connector on the left fender (X11). After July 1993 it was removed.
We usually would use a scanner on your car and I couldn't remember. If you use your multimeter set on duty-cycle you can monitor the on-off ratio that is used to monitor closed loop operation. If you monitor pin# 3 you should get a duty-cycle that ranges up and down around 50%. It should oscillate within 20% maximum. In other words it shouldn't go above 60% or below 40%. The rapidity of the oscillation is important but not quantifiable.
With a scanner one can also monitor the actual O2 sensor voltages, which are rather difficult with out break out boxes or leads.
If you are real adventuresome I will describe again a method for pulling fault codes from the diagnostic connector (on right fender) without an impulse counter or scan tool.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 05-28-2000).]