What are the causes of engine shaking and unstable idle speed?

[HaleyAnn]

Engine shaking and unstable idle speed can be caused by the following reasons and solutions: 1. Excessive engine carbon deposits: When there is too much carbon buildup inside the engine, the gasoline sprayed by the fuel injector during startup will be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture and difficulty starting. The vehicle will only start easily once the carbon deposits have absorbed enough gasoline to reach saturation. Solution: Regularly clean engine carbon deposits. 2. Air filter: Failure to replace it in time can lead to insufficient air intake, reducing engine idle speed and causing engine shaking. Solution: Replace the air filter. 3. Low ignition energy: During cold starts, the engine's internal temperature is insufficient, requiring the fuel injector to spray more gasoline to meet power demands. Fuel needs higher ignition energy, and increased spark plug gap can lead to reduced ignition energy, subsequently affecting performance and causing vehicle shaking. Solution: Replace the spark plugs. 4. Abnormal water temperature: High engine water temperature can cause ignition timing to advance, altering the air-fuel mixture ratio and thinning the engine oil viscosity (reducing lubrication). Causes of abnormal water temperature include insufficient coolant, a stuck thermostat, fan malfunction, or inaccurate temperature control switch readings. Solution: It is recommended to visit a 4S shop for inspection and repair.

[KatherineDella]

Engine shaking and unstable idle speed, I've encountered this several times. The most common cause is worn-out spark plugs failing to ignite properly, causing violent shaking. If the fuel injector is clogged, leading to poor fuel spray, the lean air-fuel mixture results in unstable RPM. Intake manifold leaks are another culprit – cracked hoses allow excess air into the engine, disrupting combustion balance. Severe engine carbon buildup blocking the combustion chamber also messes up idle. When oxygen sensors or mass airflow sensors fail, the ECU miscalculates the air-fuel ratio, making the car tremble like having indigestion. For simple checks, inspect spark plug color – replace if blackened. For complex issues, use an OBD scanner to read trouble codes. Repair promptly to avoid stalling hazards. Safety first – don't save pennies only to spend dollars on major repairs later.

[DePiper]

Engine shaking and unstable idle can have multiple causes. Worn-out spark plugs failing to ignite properly can cause noticeable shaking. Carbon buildup clogging the fuel injectors leads to uneven fuel supply, making RPM fluctuate. Cracks in the intake manifold causing air leaks disrupt the air-fuel mixture. A stuck or faulty idle control motor means the system can't maintain proper idle. Low fuel pump pressure or a dirty fuel filter restricting fuel flow can also be culprits. Carbon deposits in the throttle body or combustion chamber reduce efficiency. The shaking often worsens when AC places extra load on the engine. DIY solutions like cleaning the throttle body or replacing the air filter might help. If problems persist, consult a professional mechanic to ensure driving safety - don't delay repairs.

[LaOwen]

Engine shaking and unstable idling, often noticeable when parked, can be unsettling. It is usually caused by ignition system issues, such as worn-out spark plugs failing to ignite. Dirty fuel injectors disrupting fuel delivery can also be the culprit. Excessive carbon buildup inside the engine leads to incomplete fuel combustion. Problems with the idle control system, like a stuck control valve, can cause erratic RPM fluctuations. Faulty sensors, such as a malfunctioning oxygen sensor, may cause the ECU to incorrectly adjust the air-fuel mixture. Address these issues promptly to avoid stalling accidents. A quick check involves inspecting spark plugs for blackening and replacing them if necessary. For safety, don’t delay—visit a professional shop for a thorough inspection to ensure reliability.