Why does the Kia Forte shake intermittently after idling?
2 Answers
The reasons why the Kia Forte shakes intermittently after idling are as follows: Severe engine carbon deposits: The most common cause of car shaking is a dirty throttle body or excessive carbon buildup in the fuel injectors. When there is too much carbon deposit inside the engine, the gasoline sprayed by the cold-start injector will be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start. In this situation, the engine can only start easily after the carbon deposits have absorbed enough gasoline to reach saturation. After starting, the gasoline adsorbed on the carbon deposits will be sucked into the combustion chamber by the engine's vacuum, making the air-fuel mixture too rich. The combustible mixture in the engine alternates between being too lean and too rich, causing the engine to shake during idle after a cold start. The lower the temperature, the more fuel is needed for a cold start, and the presence of carbon deposits will significantly affect whether the cold start proceeds smoothly. Ignition system issues: Check the condition of the spark plugs, high-voltage wires, and ignition coils. Poor performance in the ignition system or suboptimal spark plug firing can also lead to this type of fault.
I've been driving for over a decade and have encountered similar issues with my own car. When the engine idles for a while and then starts shaking, the most common cause is ignition system problems, such as aging spark plugs or unstable ignition coils. At idle, the engine load decreases, and if the spark plugs fire irregularly, it can cause engine vibration. Another possibility is a dirty throttle body, where carbon buildup can restrict air intake, making the shaking more noticeable as the temperature rises slightly after idling. I recommend starting with simple checks: see if the spark plugs need replacement—they typically should be changed every 2-3 years—and clean the throttle body. Don't ignore this issue, as it can lead to increased fuel consumption and, if left unfixed long-term, even affect engine lifespan. Regular maintenance can help prevent these problems.
