The computers that control combustion in today's vehicles supposedly aren't affected by such things.
Actually, the engine computer system can only control two parameters.......fuel mixture.....and ignition timing (at any given throttle setting, determined by the driver). Neither of these effect volumetric effeciency to any great extent, or the output of pollutants, vis-a-vis outside air temperature. Modern engines do not have any means of preheating or cooling the intake air which is fed to the throttle body and ultimately the combustion chamber.
The colder the intake air is, the more efficiently the engine runs, and the more horsepower it will generate....which is why, if you ever hang around a dragstrip, you'll see the pit crews packing ice bags on their vehicles intake manifolds before a run.
Most of the major automakers have/are experimenting with systems to accomplish this function (using the vehicles' air conditioning system) in an attempt to eliminate the expensive catalytic converters, but so far (to my knowledge) nobody's made it work yet.
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