What Causes the Car to Shake When Accelerating in Third Gear?

[Declan]

Analysis of Car Shaking During Acceleration: 1. Cold Start Shaking: The primary reason for car shaking during a cold start is incomplete fuel combustion, leading to insufficient power. Low ignition energy requires more throttle input to meet power demands during startup, especially when fuel and lubricant temperatures are low. Over time, the spark plug gap gradually widens, reducing ignition energy and causing poor fuel atomization, which results in car shaking. Additionally, aging ignition coils or spark plug high-voltage wires, as well as electrical leakage, can also reduce ignition energy. 2. Shock Absorber System Issues: Car shaking can also be related to aging shock absorbers. These components are responsible for filtering out engine vibrations during operation. If the shock absorbers fail, these vibrations can directly transmit to the steering wheel and cabin, affecting driving. When the engine is idling, turning on electrical systems inside the car can easily cause shaking. The engine load increases due to the electrical systems, causing the idle speed to drop. To compensate for this, the engine automatically raises the RPM slightly. Therefore, when electrical systems, especially the air conditioning, are turned on, the engine often shakes. This shaking is likely due to aging shock absorbers and requires timely replacement. 3. Tire Issues: When replacing tires or rims, it's essential to perform tire balancing. Otherwise, uneven weight distribution can cause the steering wheel to shake. If uneven weight distribution is detected, lead weights should be added to the inner side of the rim to balance the tire weights. Both standard steel rims and lightweight aluminum rims can deform or crack under certain external forces. Deformed rims can cause shaking while driving, as can uneven rim weight distribution or incorrect rim angles. 4. Throttle Issues: The most common cause of car shaking is a dirty throttle or excessive carbon buildup in the fuel injectors. After driving a certain distance, a dirty throttle may not close properly or may get stuck, causing high idle speed. Carbon buildup in the engine can also lead to car shaking, especially during startup, when the engine shakes more violently than usual or even fails to start on the first try. Therefore, when the car shakes, the throttle and fuel injectors should be inspected first. If they are dirty or have excessive carbon buildup, they should be cleaned promptly with throttle or injector cleaners. 5. Unstable Oil Pressure: If the engine carbon has been cleaned, the throttle washed, and the gaskets replaced, but the car still shakes, it's recommended to check the fuel supply pressure and the intake pressure sensor at a repair shop. Abnormal fuel pump pressure or incorrect intake pressure sensor readings can also cause car shaking.