Causes When Car Shakes at Idle but Smooths Out While Driving 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 6 Reasons Your Car Is Vibrating When Idle or Stopped Sun Devil Auto What could be the cause of engine vibration when idling? 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, Car Shaking at Idle: 8 Causes and When to See a Mechanic (2026 Guide)