Reasons for Engine Shaking at Hot Idle Speed
2 Answers
Engine shaking at hot idle speed can be caused by faults in the intake system, fuel system, ignition system, electronic control system, or mechanical structure. Below is an analysis of the reasons for engine idle shaking: 1. Intake system fault: Excessive carbon buildup in the throttle body or intake manifold, or a clogged air filter element, reduces the cross-sectional area of the idle passage, leading to less air entering the cylinders than normal. This results in a richer air-fuel mixture, incomplete combustion, and engine shaking. 2. Fuel system fault: Abnormal fuel supply pressure can be caused by various factors, such as a clogged fuel filter, damaged fuel pump or clogged pump screen, insufficient fuel pump pressure, weakened fuel pump safety valve spring, or damaged fuel pressure regulator. Incorrect fuel pressure leads to an overly rich or lean mixture, reduced engine performance, and shaking. 3. Ignition system fault: Spark plugs introduce high voltage into the engine combustion chamber and generate sparks between electrodes to ignite the air-fuel mixture. If the spark plug electrode gap is incorrect, carbon buildup or erosion occurs on the electrodes, or the spark plug insulator is cracked, the spark plug may fail to fire or produce weak sparks. This results in poor combustion, uneven engine power output, and engine shaking.
I've been driving for over 20 years, and the most common cause of engine shaking at idle when warm is carbon buildup, especially sludge accumulation in the throttle body or intake manifold, which affects unstable airflow. Worn spark plugs or faulty ignition coils can lead to uneven combustion, causing the entire engine to vibrate. Additionally, clogged fuel injectors or low fuel pressure resulting in inaccurate fuel injection can also cause shaking. If the engine mounts are aged and ineffective, they can't absorb vibrations, transmitting them into the cabin and even making the steering wheel shake. A dirty mass airflow sensor giving incorrect readings can also cause ECU adjustment issues. Slight shaking at idle might be fine, but persistent and severe shaking is dangerous, as it can easily lead to stalling at red lights and cause accidents. I recommend regularly cleaning the throttle body and checking the spark plugs—don't wait until it affects driving to address it. Using high-quality engine oil and fuel additives can help prevent carbon buildup. If shaking becomes noticeable, take it to a professional shop to have the mechanic read the trouble codes for diagnosis. In short, warm-engine shaking involves multiple systems, so troubleshooting should be thorough.
