I hooked up an Autometer A/F ratio gauge to the O2 sensor in my 91 300SE. With the engine at operating temperature, I get the following period measurements:

700rpm - 3 seconds
2000rpm - 1 second
3000rpm - 0.5 seconds
etc.

These are not precision readings.

Other observations - the gauge shows lean when accelerating and goes off the scale on the lean side when decelerating.

Does this sound like a healthy O2 sensor?

The car has 146K miles. I don't know how old the O2 sensor is since I don't have a documented history of the car.

My complaints are a few seconds of stumbling when started and a minorly rough idle at operating temperature. The engine is practically silk above idle. I have no problem with the way it accelerates or decelerates... certainly no problem a V8 wouldn't solve.

I'll pursue this further with a VOM. What min and max voltages should I see?

Thanks,
Sixto
91 300SE
87 300SDL

http://www.flash.net/~lorint/lorin/fuel/oxybench.htm