What Causes Engine Shaking at Idle Speed?

[Barbara]

Engine shaking at idle speed is likely due to severe carbon buildup in the engine. Here is more relevant information: 1. Ignition System Issues: Problems with the ignition system can also cause vehicle shaking at idle, typically due to excessive carbon deposits on the spark plugs. 2. Troubleshooting Methods for Shaking Issues: (1) Inspection of the Idle Control Motor: Turn the ignition switch to position 1, and you should hear the motor operating. If no sound is heard, repair or replace the idle control motor, ECU, and related wiring. If sound is present, proceed to the next step. (2) Inspection of the Throttle Potentiometer: Measure the voltage between pins 8 and 7 of the throttle control component; it should be approximately 3.8V and remain unchanged regardless of throttle position. If the voltage is abnormal, repair or replace the throttle position potentiometer. If the voltage is normal, check the wiring between the throttle position potentiometer and the ECU. If the wiring is normal, repair or replace the ECU. If the wiring is abnormal, repair or replace the wiring. Also, verify that the vacuum hose connection between the fuel distributor and the throttle body is secure.

[Danielle]

Last time my car was idling very roughly, and after checking, I found several most common causes. One is excessive carbon buildup in the throttle body; over time, dirt accumulates and blocks the air intake, causing the engine to inhale insufficient air and resulting in uneven shaking. The second is aging spark plugs or issues with the ignition coils, where irregular ignition directly affects combustion efficiency. The third is a dirty fuel system, with clogged fuel injectors leading to uneven fuel supply. Additionally, aging or loose engine mount rubber pads can make vibrations more noticeable. Also, vacuum hose leaks can cause unstable idling. For diagnosis, I recommend starting with the simpler steps: clean the throttle body, inspect and replace spark plugs, and for older cars, pay attention to the mounts and fuel line connections. Rough idling affects driving comfort and mechanical lifespan, so timely action can prevent major repairs.