Can you explain what you mean by "vibrates"? Does it feel like the engine is rough idling? If you press very lightly on the accelerator when this happens, does it go away? If not, perhaps loose exhaust.I have a 2008 BMW 528i. It has 85 thousand miles on it. Overall the car runs great, but I can't figure out why it vibrates so much when I'm idle, like at a light. Any ideas?