I have a 2009 Cooper S with about 95,000 miles. Earlier this week it started to not accelerate properly, rough idle and misfires. This happened the first time this car has ever been exposed to below freezing temps. The code was P0304. I left it parked in the garage yesterday to deal with it today. Went out this morning and it would not start at all. After a little reading, I moved the coil pack from cylinder 4 to 3 and the car started right up. The code changed to P0303. At this point should I replace just the coil or the spark plugs too? To my knowledge, neither of these items have been replaced on the car. TIA

 

If you have no knowledge of the plugs ever being done, I would do the spark plugs and start with one coil, but I find it weird that one cylinder fault would keep the car from starting. Has the car ever had a carbon blast done?

 

+1 on the carbon cleaning. I did mine yesterday after having rough idle and misfire/rich/O2 codes thrown on startup for months, to the point where it flooded out on a cold morning and wouldn't start for two days. Now it starts and runs perfect.