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I have a short ram intake in my car, and have been hand-tuning the fuel maps. One issue I ran into, took me a while to figure out, is that my fuel maps would be a few percent lean in the morning and 6-10% rich in the afternoon. I finally figured out why - intake air temperature was much higher in the afternoon, resulting in lower air density (at the same pressure), which threw the maps off. Having warmer, less dense air gives (in theory) better combustion but more importantly it allows the throttle plate to be open a bit more, which cuts down on some parasitic losses and gives better fuel economy.
It's not true for every vehicle, but broadly speaking colder air = more power, worse economy, and warmer air = less power, better economy.
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