Quote:
Originally Posted by a.graham52
the colder the air the worse your fuel economy but the better the power, the denser the air, the more fuel added to keep a good fuel mixture going, the warmer the air the "leaner" the air mixture will be so fuel is subtracted. ....
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Warmer air is less dense, but the O2 sensor compensates for colder air and still brings the AFR to 14.7.
With more power available, the engine can run at a slightly lower rpm, which works to balance out the extra fuel added.
Hot enough air will cause the PCM to reduce timing, which can also adversely affect economy, and require a higher rpm to make the same power, which can increase wear.
Most savings with warm air are when the engine is started cold, then there is definitely fuel saved and lower emissions. Not so much after fully warm, especially in hot weather.
Driving habits and how the PCM is tuned, high-flowing exhaust all make a difference.