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 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, M120 V12 rough idle and vibration is this normal?, I have a Mercedes Benz W140 S600 with the M120 V12 engine., I know this engine is supposed to be very smooth, but mine has noticeable vibration at 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