My 2010 Cooper automatic had a misfire on a particularly cold day. It didn't re-occur for 5 days, but the yellow engine light stayed up. I put in a bottle of Techron, filled the tank with fuel and drove it for 120 miles, and today the warning light went away.
A nice solution to my particular problem.

Incidentally, I had stopped at my MINI dealer earlier, and the service rep told me that if I were to drive it steadily at 50 MPH, at just below 2,000 rpm, for 50 or so miles, without a misfire it would probably clear. I had done just that on the day that it did clear, on the expressway.

That might be useful to know.