Does Your Car Shake at Idle but Smooth Out While Driving? Here's Why Steering wheel vibration while idle. Is your car vibrating when idle? Here's when you should be worried What could be causing a slight whole car vibration when idling? 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