To test the lambda on my 1988 300SE I ran the car for about 6 miles and got it up to normal operating temp. Drove home, popped the hood and with the car idling in park took out my new Sears multimeter and set it for duty cycle and % and got the following readings: pin#3 constant 20.7; pin#4 84.3 to 86.6 with it constantly changing. I turned the car off, restarted and revved it a bit, and at idle got the same results.

Question 1. On my car is it pin 3 or 4 I should test? When I went back through prior posts I see reference to both pin 3 and 4. There's no way my car should be steady at 20.7 and I mean steady for 45 seconds, it never changes. It also does not appear to be a fault code.

Question 2. Isn't this a rather lean setting if pin 4 is correct?

I should mention I made certain of a good ground before testing duty cycle.

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Thanks,
Ron Brooks