Why does the engine have high idle speed when cold?
1 Answers
If the idle speed is around 1500 rpm when the engine is cold and gradually decreases as the engine coolant temperature rises, eventually stabilizing between 600-800 rpm (idle speed varies by vehicle), this is a normal phenomenon. The reasons for high idle speed when cold are as follows: 1. A cold engine refers to when the engine has cooled down. When cold, due to the low temperature inside the cylinders, gasoline atomization is poor. To meet the necessary combustion conditions, the electronic fuel injection system will increase the concentration of the air-fuel mixture. Therefore, the engine raises the idle speed to increase fuel injection and enhance the mixture concentration. 2. As the cylinder temperature increases, an overly rich air-fuel mixture is no longer needed, so the idle speed gradually decreases, and the engine's fuel injection also reduces accordingly. Once the engine temperature fully normalizes, the ECU maintains an optimal air-fuel ratio of 14.7, which is the perfect proportion for complete combustion of air and fuel. At this point, the engine enters closed-loop operation, where fuel injection is no longer based on the coolant temperature sensor but adjusted according to the oxygen sensor levels in the catalytic converter to achieve complete combustion and optimal emissions.
