What Causes Severe Engine Shaking and RPM Drop During Idle?
2 Answers
Below are the specific reasons for severe engine shaking and RPM drop during idle: Clogged Catalytic Converter: A clogged catalytic converter can lead to poor exhaust flow, reduced power, increased fuel consumption, and in severe cases, engine shaking or even stalling. Faulty Spark Plugs: Faulty spark plugs can cause idle shaking, noticeable power loss, increased fuel consumption, and may trigger a series of engine misfire symptoms (such as backfiring, black smoke from exhaust, severe vibration, etc.). Throttle Body Carbon Buildup: Carbon buildup is the main factor affecting throttle body performance. Not cleaning the throttle body for extended periods can cause errors in throttle opening and allow contaminated air to enter the engine cylinders, resulting in abnormal engine operation.
When the car idles, the RPM drops and it shakes badly. The most common reason is too much carbon buildup in the engine, especially if the throttle body or fuel injectors are clogged. My old car had this issue before—unstable idle, erratic tachometer, and it felt like the engine was wobbling when driving. Other causes could be worn-out spark plugs or faulty ignition coils, leading to misfires and RPM drops. Fuel system problems, like a weak fuel pump, insufficient fuel injection, or a faulty mass airflow sensor causing incorrect air intake, can also trigger this issue. Additionally, as the car ages, worn engine mounts fail to absorb vibrations, making the shaking worse. I’ve found that such problems shouldn’t be ignored—first, try cleaning carbon deposits or replacing spark plugs. If that doesn’t work, consult a professional to check voltage and sensors. Regular maintenance, like cleaning the throttle body every six months, can prevent 90% of similar issues.
