What Causes Unstable Idle Speed and Obvious Body Shaking When Starting the Car?
2 Answers
Reasons for unstable idle speed and obvious body shaking when starting the car are as follows: Low ignition energy causing shaking: The first issue a car faces during cold start is low temperature. The engine's internal temperature is insufficient, and both fuel and lubricating oil temperatures are inadequate. Therefore, during cold starts, more fuel should be injected to meet power requirements. The larger the spark plug gap, the smaller the ignition energy. At low temperatures, fuel atomization is poor, requiring higher ignition energy. Over time, the spark plug's ignition gap tends to increase, leading to reduced ignition energy, which affects power performance and causes the car to shake. Inappropriate air-fuel mixture causing shaking: If the air-fuel mixture ratio in the car's engine compartment is not accurately adjusted, the car is prone to shaking. In closed-loop control cars, the oxygen sensor's minimum operating temperature is 370 degrees Celsius. If the car has just been started, the exhaust pipe temperature does not reach 370 degrees Celsius, so the oxygen sensor does not work. At this time, the ECU makes incorrect judgments, leading to errors in controlling the air-fuel mixture and ignition timing through its actuators, thereby reducing the car's power output and causing shaking.
Recently, my car has been experiencing unstable idling after startup, with severe body shaking. After some DIY troubleshooting, I suspect it might be an engine ignition issue. Worn or dirty spark plugs failing to ignite properly can cause uneven engine operation, leading to vibrations. Faulty ignition coils are another common culprit, as they disrupt current transmission. Additionally, clogged fuel systems—like severely carbon-fouled fuel injectors—can prevent proper fuel spray, while restricted airflow also disrupts the air-fuel ratio balance. Carbon buildup in the throttle body hinders smooth air intake, resulting in significant idle fluctuations. If left unaddressed, fuel consumption will rise and accelerate part wear. I recommend starting with a simple spark plug replacement for initial diagnosis; if that doesn’t help, visit a repair shop for a full system check. Regular maintenance can prevent such issues, especially for older vehicles requiring extra attention. Safety first—don’t let shaking compromise driving stability. Now, consult your parts manual or online resources to brush up on knowledge.
