I have a 99 A4 Quttro 5 speed. The engine is mis-firing or idling very rough. I have found that one of the ignition coils is not firing. It's not the coil since i've tested with a known good one. All other coils test OK. What drives the coils (ignition control module, igniton amp). Any suggestion on what could be the problem? and how to test these areas. Also, if I need to take to dealer how much will it cost. If I can repair it my self I will try, I don't have any special tools besides regualr shop tools. Any help is appreciated.