Why does the vehicle shake when starting?
3 Answers
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.
When it comes to engine shaking during startup, I often encounter this issue with older car models. The main cause is an inefficient ignition system, such as dirty spark plugs or worn ignition coils, leading to misfires and engine vibration. Excessive carbon buildup affecting combustion efficiency can also cause shaking, and clogged fuel injectors worsening fuel delivery exacerbate the problem. It's more noticeable in cold weather because thick engine oil provides poor lubrication. Regular maintenance like replacing spark plugs and cleaning the throttle body is recommended. Checking spark plug condition is easy to do yourself—replace them immediately if you find cracks or carbon deposits. If shaking is accompanied by unusual noises, it might indicate damaged engine mounts that need repair, otherwise vibrations will transfer into the cabin making it more uncomfortable. Using good fuel additives to clean carbon deposits helps achieve smoother startups and extends vehicle lifespan—don't wait until minor issues turn into expensive major repairs.
As a regular office worker commuting daily, I used to be troubled by engine shaking during startup. A mechanic friend later explained it's often due to aging spark plugs causing unstable ignition. Cold weather exacerbates the issue as insufficient engine lubrication makes shaking more likely. Fuel-related problems like using low-grade gasoline or partial injector clogging leading to uneven fuel supply can also be culprits. A dusty air filter restricting airflow causes oxygen-starved combustion and subsequent tremors. I've even experienced vibrations transmitted to the car body from loose engine mounts. The solution is starting with simple steps: inspect and replace the air filter every six months, change spark plugs every 20,000-30,000 km. Using qualified fuel minimizes sludge buildup – now my car starts smoothly with better fuel efficiency than before. Regular maintenance saves both hassle and money while preventing roadside breakdowns.
