>> “Cars with computer engine management system actually shut off the gas going to the engine while coasting” <<
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I have five vehicles with ‘computer’ engine management systems, and none of them do that.
There is really no need to have fuel going into the cylinders when coasting. With the emphasis in recent years on mileage, I don't see why any manufacturer wouldn't do that. I probably should have qualified my remark with weasel words like "recent" and "many".
My current car (manual transmission) has a real-time readout of instantaneous mileage, and it definitely goes to "infinite" when coasting in gear, and to a high, but finite number (e.g. 120 mpg) when coasting in neutral. My previous car didn't have this readout, so it would be impossible to tell without a scanner plugged into the OBD port.