I did a bunch of searching but most of what I've found is people discussing the Cooper S. My wife's car is a 2013 base model cooper (Justa) with 52K miles.
We're in the Northeast USA so it's cold at night and the car sits outside.
A couple weeks ago she got a check engine light on a short drive to the gym so I pulled the code. There were a couple codes and a couple of pending codes (random misfire, cylinder 3 misfire, cylinder 4 misfire). The car seemed to be running OK. I cleared the codes, filled the car up with 93 (like we always do), and added some Techron fuel system cleaner.
Everything was fine for a couple weeks.
This morning when my wife started up the car she said it was running rough. About a half mile down the road the Half Shaded Engine Reduced Power warning came on so she turned around and came home. I pulled the codes, but there was only one pending code for cylinder 4 misfire....no confirmed codes. I cleared the code and went for a drive. Everything seems fine.
Any advice?
I'm thinking I'll throw some new spark plugs at it but beyond that I'm not sure how to proceed.

 

b4 you change plugs, swap coil from cyl 4 with another. if the misfire code follows it to the new cyl then replace the coil.

 

+1
My car was acting wierd with this cold weather. I eventually lost a coil pack 15 miles away from home. Also the airbag light was coming and going. Now that the weather is a bit warmer (above freezing lol) aorbag light doent come on. New coil pack was the fix for my issue...good luck