I attempted to use my Fluke meter as you described and I think my meter is slightly different than what you are describing. By pressing the "Hz" button twice the meter goes into the RPM mode for 2 cycle engines, by pressing the polarity button at this point does nothingand the reading is in the thousands.
My fluke meter has a %Duty/ms-Pulse button which goes directly into a duty cycle reading when pressed once, which is what I am doing. I was told that to check whether or not the reading is right pull off a coolant sensor and the reading should be a steady 30%, which is what I am getting after starting up a warm engine.
One thing I did notice when hooking my meter to socket #3 is the voltage is different when I have a constant 60% reading and ALL other times (even when I pull off the coolant sensor plug. I get a constant reading of approximately 5.5 volts before pressing the %duty cycle button when the percentage is 60% as opposed to approximately 9 volts at all other times. I checked the input voltage at the control box and in all cases it is 13+ volts (engine running).
I am testing the sensors as per the Mercedes manual and so far the following seem OK Full Load Contact OK Coolant Sensor OK Airflow Sensor OK O2 Sensor OK TD-Signal OK Altitude Sensor OK Idle Speed Contact Am trying to test but so far am unable to make the engine "Hunt" when activating the swicth with the engine running at 2500 rpm. Also when testing the current at the Electrohydralic Actuator the reading doesn't swing to -60ma when releasing the throttle from 2500rpm.
I hope I am explaining things clearly. And thank you for your patienence with this problem.
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