What Causes Engine Shaking When Starting an Automatic Car?

[MacAlexis]

Here are the reasons for engine shaking when starting an automatic car: 1. Throttle: A dirty throttle causes uneven airflow, leading to shaking. 2. Fuel system: Poor fuel flow results in inadequate fuel supply at low throttle, causing uneven cylinder operation and shaking. 3. Transmission: Abnormal transmission operation. 4. High-voltage wires: Broken or burnt high-voltage wires or spark plug failure can cause cylinders to misfire, leading to unstable engine operation and shaking. 5. Battery voltage: Whether the battery voltage is within the specified range. Below are additional details on related causes: 1. Cause: The most common reason for car shaking is a dirty throttle or excessive carbon buildup in the fuel injectors. 2. Engine carbon buildup: When there is excessive carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start.

[OKhloe]

I've been repairing cars for many years and have dealt with numerous cases of engine shaking during automatic transmission vehicle starts. The most common issue is problems with the ignition system, such as severely worn or aged spark plugs, or failing ignition coils causing uneven ignition, which leads to unstable cylinder operation. The fuel system is also a critical factor; clogged fuel injectors or overdue fuel filter replacements can result in irregular fuel injection, affecting combustion efficiency. In the air system, excessive carbon buildup in the throttle body or a dirty air filter can disrupt air intake, causing an imbalance in the air-fuel mixture. Transmission components like a deteriorating torque converter or worn clutch plates can also lead to uneven power delivery, resulting in shaking. Additionally, aged or loose engine mount rubber can amplify vibrations by losing its damping effect. My advice is to first check simple components like spark plugs and filters and try replacing them yourself. If that doesn't work, use a diagnostic tool to check for error codes and take the car to a professional repair shop promptly to prevent further engine damage. Regularly using high-quality gasoline and adhering to scheduled maintenance can effectively prevent such issues.