10 Possible Reasons Your Car Vibrates When It's Idle Is your car vibrating when idle? Here's when you should be worried Why Is My Car Vibrating When Idling? WHY YOUR CAR SHAKES WHEN IDLING If your car feels smooth while driving but starts vibrating or shaking at a stoplight, something isn't right. At idle, the engine runs at its Why Does My Car Shake at Idle but Smooth Out While Driving? Why Does Your Engine Vibrate at Idle? Noticing your engine shaking or vibrating while idling? This could mean something isn't right under the hood. Here's what might be causing it and how