Is there a difference between diesel engines and gasoline in this regard? Im thinking of a phemomena called"engine braking" moreso with trucks where gearing down actually uses engine resistance to reduce speed, implying that the engine is coasting out of sync with tire rotation and in finding equilibrium, one sees black smoke spewing from diesels in these situations, suggesting the engine is active, even when decelerating.
trucks are manual, so perhaps the crankshaft is directly linked to tire rotation, but automatics....im no engineer, but methinks the power flow is one way, therfore fuel injection is governed by the load being placed on the engine, not always speed (i.e., tire rotation) and in automatics the air conditioner, alternator, fuel pump etc. still require an actively running engine.
so the engine, in the case of an automatic, is being fueled at a minimum of idle rpm. my assumption is that an automatic tranny cannot transfer power back to the engine, (i.e. would it need two torque converters at either end? etc.)