What Causes High Idle Speed in Cold Engine During Summer?

[CharlotteDella]

Reasons for high idle speed in cold engine during summer: A cold engine refers to a state where the engine has cooled down. When the engine is cold, due to low temperature in the cylinders and poor gasoline atomization, the electronic fuel injection system increases the concentration of the air-fuel mixture to meet combustion requirements. Consequently, the engine raises the idle speed to increase fuel injection, thereby enhancing the mixture concentration. As the cylinder temperature rises, the need for an overly rich air-fuel mixture diminishes, leading to a gradual reduction in idle speed and fuel injection. Once the engine reaches normal operating temperature, the ECU maintains an optimal air-fuel ratio of 14.7, which is the ideal proportion for complete combustion of air and fuel. If the idle speed is around 1500 RPM in a cold state and decreases as the engine coolant temperature rises, eventually stabilizing between 600 to 800 RPM (idle speed varies by vehicle), it is considered normal.