Why does the engine idle speed increase after a cold start?

Many car owners wake up in the morning and start a car to go to work. They often find that after the car starts, the idle speed will be higher than normal. Even accompanied by jitter or noise, and after a brief "abnormal", the engine will recover as before, which can not help but worry that the engine is not a fault?

In fact, it is a normal phenomenon that the car engine idle speed increases after the cold car starts. It is a car-to-engine protection measure and also aims to improve the combustion efficiency and emission standards. This phenomenon will vary according to the climate and temperature. For example, in the northern China or in an extremely low temperature environment, the idling speed of the car after start-up is large and long; otherwise, the outside temperature is high and the engine starts. Afterwards, the speed of idling will also be very small, even if it is not noticeable.

Because the normal working water temperature of the engine is around 90°C, in the extremely low temperature environment, the water temperature sensor will transmit signals to the ECU after the engine is started. The engine will increase the fuel injection quantity and intake air quantity, and increase the engine speed so that the engine can quickly enter normal The operating temperature. As the engine temperature gradually increases, idle speed will gradually drop to normal.

In addition to preheating the engine, the preheated three-way catalytic converter also occupies certain factors. The three-way catalytic converter is equivalent to a car purifier. Its working environment is more demanding than that of the engine. The minimum is 250°C or higher, and 400°C-800°C is the best. If it is lower than this standard, the purification effect of the exhaust gas will be affected and the exhaust gas emission will not reach the standard.

Under normal circumstances, in most parts of the country, after the cold start of winter vehicles, the idle speed rises to return to normal, which may take a few minutes, and almost no idling abnormality is felt in summer. Of course, even in the winter, we do not need to wait until the idle speed is completely stable before starting the vehicle. This will waste fuel and increase carbon deposition. In the winter, after the cold car starts, the local hot car is about 30 seconds, and it can be about 10 seconds in summer. The purpose of the car hot car is to allow the oil to fully cover the various components in the engine.

However, if the water temperature of your car's engine is normal, if the speed of the car's engine continues to rise, or if there is noise or vibration, then you have to go overhaul.