What Causes Persistent Engine Shaking?

[DiKinsley]

Persistent engine shaking can be caused by a dirty air filter, broken high-voltage wires, worn-out spark plugs, low idle speed, or clogged fuel injectors. Dirty Air Filter: The air filter is designed to protect the engine and reduce wear. It typically needs replacement every 10,000 kilometers. If not replaced in time, insufficient air intake can lead to low idle speed, causing the engine to shake. Simply replacing the filter can resolve this issue. Broken High-Voltage Wires: Broken high-voltage wires refer to the internal conductor being severed, which can affect ignition and cause engine shaking. Use a multimeter to measure resistance and replace the wire with significantly higher resistance (several times the normal value). Worn-Out Spark Plugs: Spark plugs have a limited lifespan. After 30,000–40,000 kilometers, their ignition efficiency noticeably declines, affecting engine performance. This is a common issue—replacing all spark plugs will solve the problem. Low Idle Speed: The engine's idle speed is preset in the ECU. When RPM drops below a certain threshold, the car's computer automatically adjusts it. If the idle speed is too low and causes shaking, it means it has exceeded the ECU's control range. Some vehicles have an idle adjustment screw on the throttle body, while others do not. For non-adjustable vehicles, inspect the idle control valve, throttle body, mass airflow sensor, vacuum sensor, and ignition timing (for distributor-equipped cars) to increase idle speed. Low coolant temperature can also cause low idle—check or replace the thermostat if needed. Clogged Fuel Injectors: Fuel injectors in EFI vehicles are critical components for fuel delivery and have a long lifespan (hundreds of thousands of kilometers). However, deposits in gasoline can clog the injector nozzles, leading to uneven fuel distribution among cylinders and causing engine shaking. The solution is to remove and clean the injectors.