Assuming your car's sensor is similar to my 87, 260E.

At idle, the middle terminal on the sensor should be between 0.5 and 1V. Then as you gradually depress the gas pedal, the voltage should smoothly rise. There should be no erractic change in voltage.

Also for the above test, the 3 terminals of the wire connector must be connected to the 3 terminals of the sensor, so use some alligator clips.

If you dont get any voltage, check the third connector, it should have close to 5V. This 5V comes from the ECU via the wiring harness.

__________________
Saumil S. Patel