Engines consume a fixed
volume of air; the air density changes with temperature, so a cylinder will **** in more "pounds" of air when the temperature is lower. The engine adds the right "pounds" of fuel to make it burn.
Here's a simple table of density vs. temperature. Remember the correct air temperature is that as it enters the combustion chamber, not ambient. However, for giggles, if you compare the density at 100F to that at 30F, the density is 0.081/0.071=1.14, or 14% greater. As a really rough estimation and ignoring many other things,
any engine would have 14% more power at 30F than at 100F.
Air - Temperature, Pressure and Density