In all my BMW work, I have never encountered a bad coil pack...but I just did.

'05 X5 3.0 6 cyl -125k miles, I did a head gasket on it last September.

Yesterday on a cold start - 2nd of the day - It immediately started running rough and threw a CEL. I quickly stopped and read/reset codes. Codes pointed to a mis-fire in cylinder 2. I started again and immediately had the misfire again. Drove it home 3 miles on 5 cylinders.

This morning, I pulled coils and spark plugs, cleaned them, and switched 1&2 coils. The misfire moved to #1 cylinder..Bingo! I grabbed a similar coil out of my e39, installed it and misfire went away. I checked date codes on the orig X5 coils and they are from 2005, so likely original to the car. I have ordered replacements. I also did a quick, cold compression test on cylinder #2 to rule out a damaged valve or piston and it was okay at 150psi.

I probably have 3,500 miles on it since the head gasket, and it has been running great. But the mind can't help but fear the worse when I get a mis-fire.