Is the starting speed of cold car the same as idling speed

by:DEFUS     2020-05-22
We often hear that the cold start idling speed is high, but some cars do the opposite: In the winter, the idling speed is still as stable as the old dog after a cold start in a few degrees or even tens of degrees. On the contrary, in the spring when the spring is blooming, the temperature rises to more than a dozen degrees and the idling speed is even higher when the cold start. I have such a car. And I want to tell everyone: this is normal. Reasons for high cold start idling speed The cold start idle speed is mainly to quickly heat the three-way catalyst and the oxygen sensor, so that they can enter the working state as soon as possible. Because the three-way catalytic converter purifies the exhaust gas, and the data of the oxygen sensor is an important basis for the ECU to correct the injection quantity. So the sooner these components enter the state after a cold start, the sooner they can intervene in the exhaust. After a cold start, the ECU will control the throttle valve or idle motor to increase the air intake, and then inject more oil, so that the speed will go up. Due to the increase in fuel injection, more heat is generated by the combustion, and the heating of the three-way catalyst and the oxygen sensor is faster. And now many cars also delay the ignition time in order to heat the three-way catalyst and oxygen sensor faster. Why does delaying ignition have this effect? Let us illustrate: for example, when the compression stroke piston reaches top dead center, the spark plug ignites and the mixture burns. When the piston reaches bottom dead center, the mixture is basically burned out. After the ignition stroke is delayed, the spark plug still does not ignite after reaching the top dead center. After the power stroke begins, the spark plug starts to ignite after the piston runs down a certain distance. In this way, when the piston reaches the bottom dead center, the mixture is still burning, and the exhaust gas temperature of the exhaust stroke is higher in the same way, which is equivalent to using the oil in phase to quickly 'burn' the hot oxygen sensor and the three-way catalyst. Because of this, when the cold start idle speed is high, the exhaust pipe sound is also louder than the normal idle speed, because the exhaust energy is greater. Therefore, high idle speed after cold start is not voluntary, but engineers deliberately do it to meet the engine emission demand. So why is there no difference between idle speed and normal idle speed after some cars start cold? In real life, many car owners have such questions: they all say that the cold start idling speed is high, but my car has not seen the idling speed be higher than once every cold start throughout the winter. On the contrary, the cold start idling speed becomes higher after the warm weather. What is the actual cause? In fact, this is mainly caused by the cold start emission rules, because the cold start emission test does not require below 20 degrees Celsius. Since it is not required, some manufacturers no longer need to consider the cold start emission level below this temperature. Normal idle speed control will do. This not only saves fuel but also reduces noise, giving people a 'high sense'. When the temperature is higher than 20 degrees Celsius, in order to ensure the cold start emission level, it is necessary to increase the idle speed deliberately. Generally, German cars and American cars like this, while Japanese cars no matter how high or low the ambient temperature is, they should deliberately mention the speed after a cold start. Therefore, the idle speed after a cold start is the result of responding to emission regulations.
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