I bought the much talked about multimeter from Sears for $ 30.00. My 260e is a Calif car so I had to press the button at the X92 connector to give me a duty cycle reading at pin 3 of the X11 connector. I had been getting the code for the O2 sensor (5 flashes) and with the new meter hooked up I was reading approx 6.5 % at idle. When rpm was increased the reading would go to 49.99 and then steadily decrease down to 6.5%. I checked output at the O2 sensor and with engine at operating temp of 80c the output was approx 80mv. I was told it should be 450mv minimum. I changed the O2 sensor and checked with the new meter and got a reading of approx 60% and it was fluctuating like it is supposed to. With the meter hooked up as mentioned earlier (red lead to pin3, black to ground) the duty cycle reading increased as I adjusted the screw CCW. I reversed the leads (black to pin 3, red to ground) and this change in polarity resulted in an increase in duty cycle reading when screw turned CCW (leaner) and a decrease in % when turned CW (richer). I set right at 50% and idle is greatly improved and so is milage. The majority of posts on this subject call for the meter to be hooked up as mentioned in the first part of my post; am I missing something here? Regardless of the polarity, the adjustment for 50% would be the same. Initially I didn't want to believe it was the O2 sensor since I had replaced it 35k miles ago. I love driving this car but but the high maintenance is a bummer. I just replaced the tensioner after getting only 17k out of the last one and six months ago relaced a mb factory rebuilt water pump after 30k.