Service ESC, cylinder four misfire?

I've been struggling with my car for the last 7 months.

I sometimes get the service light 'Servce ESC - Service traction control' pop up after my car kind of has a gentle shaking coming from the engine. It's not running smoothly. This generally only happens if the car is sitting idle for maybe 10 minutes or so. When I'm driving, it runs fine. Now it's starting to get to the point where it feels like it's running rough even at stop lights. I've taken my car into the shop several times because after it does this the engine light comes on and says cylinder 4 misfire.

Now i've already had the ignition coil & spark plug wires replaced since all this started. It slowed down the misfires greatly but it's still acting funny when it sits idle for longer than a few minutes. I talked to a mechanic in town, and he suggested putting Cheron fuel cleaner in my tank and switching to a higher grade of gas like BP. I did some of that. I switched from Casey's premium gas to Break Time's premium gas and started to put fuel cleaner in but the problem still persists.

I know if I take it into a shop, they'll just say nothing's wrong with it. I don't really want to ignore the problem, but it's not severe enough for a shop to really notice. Maybe if I knew what to tell them? Help.