The purpose of an BMW ignition coil is to convert the low current from a car battery into enough power to ignite the fuel and start the engine. When there is a problem with an ignition coil, it will cause a range of mechanical and performance issues. The following signs will warn you that your vehicle has a faulty ignition coil and get professional help from your Dealer. http://www.spkmotorsport.com/ignition-coil/bmw-ignition-coil/