Check Engine Light

I bought a 2010 mini cooper S with just under 55,000 miles on it I had no issues I brought it to my local mechanic that specializes in minis had him go through the entire car when I bought it stated everything was great just recommended a tune up I did since then the past three or so weeks the yellow light has come on 3 times I always take it to my local auto store before going back to the mechanic each time the code reads misfire ignition coil cylinder one my mechanic has already replaced the new spark plugs and Monday I had coil one replaced and the light is back on, the car is running completely normal no shaking the only thing I noticed at start up is it idles slightly higher, Im getting really annoyed there wasn't a single issue prior to the tune up and no actual signs of any misfiring