Just a quick question. Does the O2 simple verify things are working or does it have a function relative to duty cycle. I adjusted my lambda and get about 15mpg highway or city in my 560 SEL. I installed a new O2 sensor and using its voltage adjusted lambda and dropped to 13mpg. I adjusted back and all it okay again.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car