When a car shakes or vibrates when it stops at a traffic light, it can be attributed to a few different factors:
Engine idling: When a car is at idle, the engine is running at a low speed to keep the car running while stationary. The engine's operation at low RPMs can cause some vibrations that are transmitted throughout the car's structure, leading to the sensation of shaking.
Engine mounts: Engine mounts are components that secure the engine to the car's chassis. They are designed to absorb and dampen vibrations from the engine. Over time, engine mounts can wear out or become damaged, leading to increased vibrations being felt in the car, especially when the engine is running at idle.
Imbalance or wear in rotating components: Vibrations can also be caused by imbalances or wear in rotating components, such as the engine's flywheel or the transmission system. These imbalances can result in uneven forces being transmitted through the car, leading to shaking or vibrations.
Fuel delivery or ignition issues: Problems with fuel delivery or ignition can cause irregular engine operation, resulting in vibrations. Issues like clogged fuel injectors, faulty spark plugs, or a malfunctioning ignition system can disrupt the smooth running of the engine and contribute to shaking when the car is stopped.
Exhaust system problems: A damaged or malfunctioning exhaust system, such as a loose or broken exhaust pipe or muffler, can cause vibrations and shaking. When the car is stationary, the vibrations from the engine can resonate through the exhaust system, amplifying the shaking sensation.
It's important to note that the severity of the shaking can vary depending on the specific car and the underlying causes. If you experience significant or persistent shaking when your car is stopped, it's advisable to have it inspected by a qualified mechanic to diagnose and address any potential issues.