What Causes a Sudden Shake During Car Idling?
3 Answers
Here are the reasons for engine shaking during idling: 1. Intake manifold or various valve leaks: Leakage can cause abnormal engine air intake, leading to either too rich or too lean air-fuel mixture, resulting in abnormal combustion. This may cause the engine to shake at idle. 2. Excessive carbon buildup on throttle body and intake passages: Too much carbon deposits and dirt on the throttle body and surrounding intake passages change the cross-sectional area of the air passage, preventing the control unit from precisely regulating idle air intake. This leads to improper air-fuel mixture and abnormal combustion. 3. Inaccurate air intake measurement: The control unit receives incorrect signals from the air flow sensor and issues wrong commands, causing inaccurate idle air intake and improper air-fuel mixture concentration. This results in abnormal combustion and is an indirect cause of unstable idling.
I usually drive to and from work, and occasionally my car suddenly shakes when idling at a red light, making the entire body tremble. The mechanic told me that this could be due to excessive engine carbon buildup or the need to replace the spark plugs. Carbon deposits can clog the fuel injectors, causing uneven gasoline atomization and incomplete combustion, which naturally leads to shaking. Dirty throttle bodies and restricted air intake can also cause this. I recommend regular engine cleaning, about every 20,000 kilometers, to prevent carbon buildup. Another common cause is ignition system issues, such as loose high-voltage wires or faulty coils, leading to intermittent ignition. These minor problems may seem insignificant, but if not addressed promptly, idle shaking will become more frequent and even affect fuel economy. Finally, check if the air conditioning is set too high, as it can also increase engine load. In short, a comprehensive inspection will ensure peace of mind while driving.
I often tinker with my car, and occasional shaking at idle is quite common. The most frequent cause is dirty fuel injectors; carbon buildup restricts fuel flow, leading to an imbalanced air-fuel mixture and unstable idle. Worn-out spark plugs are another factor—misfires can easily cause shaking. I've tried using fuel additives to clean the fuel system, which is cheap and effective. Additionally, aging engine mount rubber could be the culprit—if its vibration-dampening effect weakens, the shaking transfers to the car body. Don’t overlook the idle control valve; if it’s dirty, it can affect RPM stability. I recommend checking these parts during every maintenance service. Insufficient fuel pressure or a clogged air filter can also make the engine "struggle to breathe," causing occasional shaking. Prevention is simple: drive at high speeds occasionally to clear carbon buildup and avoid prolonged idling. If the shaking worsens, it’s safer to get a professional diagnosis.
