Crikey I’ve a bad memory these days! Yes, I’ve seen this before, and set the option of ECO for the ACC.
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However, I believe it impacts on the acceleration of the car up to the preset value, but not the means of deceleration when moving downhill. It depends what the objective is I guess. If you’re after top fuel economy you’ll be reading the road ahead and adjust road speed to suit while using minimum fuel. If you’re after a steady and low input drive, then ACC is the way to go.
I had an E Class Merc years ago, and the preset MPH had around +/- 10% built in. Not great to be spot on to the speed limit, but good for economy. It feels like the Cali has +/- 2mph. This causes steady acceleration (more fuel) when pulling uphill (even in ECO mode), and dropping gears (to D3) going downhill, and application of braking.
Just thinking, you might be able to adjust the preset span using an ODB2 dongle (Carista)?? My Carista licence has expired so I can’t check.