Is the replacement of the 02 sensor difficult. My gas mileage has gone to crap. Think the original 02 sensor may be on the car.

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1972 220d gone lived a good life
1972 280se gone but not forgotten
1978 300D the best i ever had
1977 350se speed racer gone
1995 honda accord lx coupe victim of the growing family
1988 300e gone but not forgotten