Why does the vehicle shake when starting?

[OAnthony]

There are several main reasons: 1. Incorrect air-fuel ratio: The air-fuel ratio is not accurately adjusted, which occurs in both open-loop and closed-loop control. In a closed-loop control environment, the minimum operating temperature of the car's oxygen sensor is 370 degrees Celsius. However, when the vehicle is just started, the exhaust pipe temperature does not reach 370 degrees Celsius, and the oxygen sensor does not start working. At this time, the ECU makes a misjudgment, leading to errors in controlling the ignition timing through the actuator, thereby reducing power output and causing the vehicle to shake. 2. Carbon deposits on the engine valves and intake passages: Carbon deposits absorb fuel. Even if the remaining fuel burns completely, it cannot achieve the required power, making shaking inevitable. 3. Different working conditions of each cylinder: After long-term use, the spark plugs of a multi-cylinder engine may have different ignition control and timing gaps. However, the EDC cannot detect this error, leading to a deviation between theory and practice. Some cylinders may have lower efficiency, causing the vehicle to shake. 4. Failure of the coolant temperature sensor: The coolant temperature sensor is one of the important bases for the computer to judge the real-time working condition of the car engine. During a cold start, the engine temperature is low, but if the coolant temperature sensor misjudges and sends an excessively high signal to the computer, the computer will inject too much fuel. The fuel quantity is smaller than normal, and shaking is inevitable.