Why does my car idle rough but drives smooth?

[Beth Murphy]

If your car idles rough but drives smoothly, it often indicates an issue with the engine or related components. Common causes include dirty or faulty spark plugs, a clogged air filter, or issues with the fuel injectors. These problems can disrupt the engine's performance at low RPMs, causing a rough idle. However, when you accelerate, the increased engine speed can mask these issues, resulting in a smoother driving experience.

Another possible cause is a vacuum leak, where unmetered air enters the engine, leading to an unstable idle. A faulty idle air control valve can also disrupt the engine's ability to maintain a steady idle speed. If your car shakes at idle but smooths out while driving, it's essential to have it diagnosed and repaired promptly to prevent further damage. Regular maintenance and addressing minor issues early can help keep your vehicle running smoothly.