I was trying to check the air flow sensor by way of the ratio. I connected up my duty-cycle reading DMM to ports 1 and 3 of the 9 pin connector on the left fender and with the key on, engine off, I was getting a solid 70%, as expected.

Then I manually deflected the air flow sensor plate roughly 10%, expecting to get a reading of 10% but it stuck to 70. Deflecting the plate all the way down, it still said 70%.

When I fully depressed the gas pedal, it went to 80%, not the expected 40%.

I then started it up and it was fluctuating between 49 and 51, sometimes as low as 47 and sometimes as high as 52, again as expected.

According to the air flow plate deflection values, WIS says to test the throttle valve switch. Assuming that is the rocker switch that's triggered with the throttle cable/actuator just rear of the fuel distributor, then it tests out fine - infinite resistance normally, <1 ohm with it tripped.

Clearly, I'm missing something here. Am I not going about this right or what? How should I really be doing this and what should I expect?

__________________
-Michael.

New owner of a 1992 300E (124.030)