What Causes Vehicle Shaking During Neutral Idle?

[MacRylee]

Vehicle shaking during neutral idle is primarily caused by severe engine carbon buildup, ignition system issues, aging engine components, and unstable oil pressure. Severe Engine Carbon Buildup: The most common reason for vehicle shaking due to severe carbon buildup is either a dirty throttle body or excessive carbon deposits in the fuel injectors. When there's too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector can be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making the engine difficult to start. Only when the carbon deposits become saturated with gasoline does the engine start more easily. After ignition, the gasoline adsorbed on the carbon deposits is then sucked into the cylinders by the engine's vacuum for combustion, making the air-fuel mixture too rich. This alternation between lean and rich mixtures causes unstable idle after a cold start. Additionally, lower temperatures require more fuel for cold starts, and carbon deposits significantly affect whether the cold start proceeds smoothly. The solution is to clean the fuel system and check the idle air control valve for carbon buildup. Ignition System Issues: Check the condition of the spark plugs, high-voltage wires, and ignition coils. Poor performance in the ignition system or weak sparking from the spark plugs can also lead to this issue. The solution is to inspect the spark plugs for excessive carbon buildup and replace them if necessary. Aging Engine Components: Vehicle shaking can also be related to worn engine mounts. Engine mounts act as the engine's shock absorption system, absorbing minor vibrations during operation. If the engine mounts are faulty, the vibrations will transfer to the steering wheel and the cabin, causing shaking during idle. The solution is to replace the engine mounts at a 4S shop. Unstable Oil Pressure: If you've already cleaned the engine carbon deposits, throttle body, replaced gaskets and spark plugs, but still experience shaking during idle, it's recommended to visit a 4S shop to check the fuel supply pressure and the intake pressure sensor for any abnormalities. Abnormal fuel pump pressure or incorrect readings and poor performance from the intake pressure sensor can also cause vehicle shaking. The solution is to check the oil pressure and replace components if necessary.