You have a misfire. Don't drive your car because you can damage your cats and those are really expensive. You need to have the car scanned and troubleshot. Most likely it's a dead coil. The way a shop will troubleshoot this is a mechanic will scan the car and see which cylinder is misfiring. Then he will swap coils with another cylinder to see if the problem follows the coil to another cylinder. If it doesn't they'll try swapping something else.
'06 Arctic Metallic 325i | Sport Package | 6MT | Dinan Stage III suspension | Dinan exhaust | 330i manifold swap! Click here!
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