Ever felt your car shaking or vibrating while sitting at a red light? That rough idle is a classic symptom, but the cause isn't always obvious. As shown in the comparison, Why Does My Car Shake at Idle but Smooth Out While Driving? What could be the cause of engine vibration 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 11 Reasons Why Your Car Shakes at Idle 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