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I tested the O2 sensor with an analog voltmeter while still plugged into the ECU. At idle the needle fluctuates between .2 and .8 volts about once per second. At 2000 RPM the needle fluctuates faster between these same voltages about every half second. Is that normal operation of an O2 sensor? It appears something is causing the motor to go rich and the O2 sensor and ECU are trying to compensate by going lean, and then the cycle repeats every second. The car was overheated severely by the previous owner (I had to have head gasket replaced). Can overheating damage the coolant temp sensor?
Dan
1989 244 automatic
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