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Originally Posted by AndreiFS
I was trying to solve a high idle condition. When I bought the car it had a low idle condition. I replaced the ICV and cleaned the buterfly. Afterwards I had a high idle problem. When I saw that the mixture adjustment had been tampered with (tower was broken), I assumed that the previous owner had raised the CO mix to compensate for low idle so I leaned it. Too much. Then the car barely ran so I enriched it again. I haven't measured duty cycle yet, the meter is on order. From what I understand I have to test at socket three and look for 50%. Is that with engine off and key on or engine on?
The previous spark plugs where the R type. I put old non-resistor type back in. I also have a new oxygen sensor which I haven't installed yet. Could that help?
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I am more familiar with the measurements on an 86'-89' M103.
You would turn the Key to the on position with the engine off. Then at the screw off cap (X11) you should connect your test leads to pins 3 and 2 and reverse them until you get a reading of roughly 70% (or 85% for a California car). This reading will not fluctuate.
Then You turn the engine on and let the coolant temp rise to 80°C.
Test in the pins that gave you 70% reading (with the engine running).
Your reading should fluctuate. If it does not fluctuate it is a fault code.
You want to achieve a fluctuateing reading around 50%
A reading of 50%/ non-fluctuateing, would mean a bad 0² sensor.
I'm not sure all this applies to 90' M103's completely but should be basicly similar.
A bad O2 sensor will not always show up in your duty cycle and can screw up your testing results and make your mixture rich as well. Try unpluging yours while you are waiting for your multi meter (it's in the passenger footwell under the carpet, under the padding, wire comming out of the transmission tunnel) to see if it has any benefit on preformance.
Also search this forum and read as much as you can on duty cycle and adjusting the mixture for your car. This link is a good start:
http://www.landiss.com/mixture.htm