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O2 Sensor Diagnostics

My car has been surging for some time now, it's very noticable when the car is
cold, less noticable when the car is warm. With the gas pedal in the same
position and under constant load, the engine surges about every three seconds.

So I took some readings on the O2 sensor. Here they are:

It has 12 VDC to the O2 sensor (I take it this is for the heater) and the
current goes from about 1.7 amps to 1.0 amps as the car warms up. The Bently
says the current should increase, not decrease, as the car warms up.

The green (signal? I guess) wire has 455 mVDC with it disconnected and the
ignition on -- O.K.

But when I pick a voltage off of it when connected to the sensor and the engine
running, it varies from 0.8 VDC to 0.29 VDC at idle. If I then rev the car with
no load on it, it changes from 0.08 VDC to 1.4 VDC. Seems like an awfully large

My question: Is the O2 sensor toast and the ECU is changing the air/fuel mixture
as told to, or is it something in the ECU and the O2 sensor is just providing
feedback to what is actually going on?

The car has 95K on it, I suppose it is the original O2 sensor. I know, you'll
tell me to replace it. But I just thought I would ask first.



91 200q

Paul Waterloo                    TEL: (860) 267-7714
HydroAire Incorporated           FAX: (860) 267-7387
875 Old Hartford Rd
Colchester, CT  06415          EMAIL: 74543.407@compuserve.com