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 2018 bmw x3 30i small engine vibration at idle, new spark plugs and MAF sensor cleaned. My car engine vibrates much when in idling speed. What might be the problem? What could be causing a slight whole car vibration when idling? 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