Why does the car shake severely when driving at 100 to 120 km/h?

[StKyle]

The reasons for severe shaking when the car is driven at 100 to 120 km/h are as follows: 1. Excessive carbon deposits: If there is severe carbon buildup in the engine cylinders, it can cause spark plug blockage and valve blockage, directly leading to shaking during idling. If the car's acceleration performance has significantly declined and the shaking is persistent, the engine cylinders need to be cleaned. 2. Fuel system failure causing unstable oil pressure: Unstable oil pressure can lead to inconsistent concentration of the air-fuel mixture, not only causing shaking but also resulting in unstable idling. First, consider replacing the fuel filter, then check the oil pressure that bypasses the fuel filter. If abnormal, the fuel pump may be the issue. 3. Aging engine mounts: If the engine shaking becomes increasingly severe but the power does not weaken accordingly, it is mostly due to problems with the engine mounts. 4. Misfire or cylinder failure: The issue lies with the engine ignition coil or spark plugs. If the ignition coil fails or the spark plugs cannot fire for some reason, the car will experience shaking.