What Causes Severe Shaking When the Car is in D Gear?

[OAvery]

Excessive Carbon Buildup: Severe carbon deposits in the engine cylinders can lead to clogged spark plugs and valves, directly causing shaking during idle. Fuel Supply System Malfunction or Unstable Oil Pressure: This can easily result in unstable mixture concentration, not only causing shaking but also leading to unstable idle conditions. Aging Engine Mounts: If the engine shaking becomes increasingly severe without a corresponding loss of power, it may be due to worn-out engine mounts. Misfiring or Cylinder Misfire: The issue often lies with the engine's ignition coil or spark plugs. If the ignition coil fails or the spark plug cannot fire for some reason, the car will experience shaking.