Abstract: An air density computer is disclosed herein for controlling the fuel injected into an internal combustion engine to maintain a desired air to fuel ratio during the engine's warm-up period. The air density computer responds to a temperature sensor, mounted in the engine's air intake manifold, and computes a density signal indicative of the relative density of the air as a function of the air's temperature. The fuel control computer responds to this density signal as well as other sensor inputs and generates output signals indicative of the engine's fuel requirements which are corrected for the higher density of the cold air inhaled by the engine during the transient warm-up period.