My '90 300E O2 sensor is about three years old.

The 260Es are geared lower and the engine turns higher RPMs.

I've noticed a good bit of variation in mileage and power in different 124 cars.

My '90 mileage was about 25 on the highway for years. A few months ago I adjusted the lambda and now it gets almost exactly 27. I would not have expected the adjustment to make an MPG difference but it did.

Our '91 300E only gets about 25.5 highway. But it has more power than the '90.

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2012 E350
2006 Callaway SC560