weed eater Briggs and Stratton mower idle surges?

The mower isn't that old. It was bought around 2009. It was used until 2011 and then put up. And then I started using it again in 2013.

While I was mowing last summer, I bumped the spark plug wire/front of engine against a picnic table, like bumped it lightly, and the mower ran funny and died. It wouldn't start, so knowing the spark plug wire was right there when I bumped into the picnic table, I unhooked it and hooked it back in, and still no start. I then unhooked the spark plug wire, turned the wire around, plugged it back, and it started running. Although it runs now, the idle seems to surge ever since this happened. Or if I'm on an incline, the mower almost dies and then idles back high. It seems to surge more on an incline. It almost sounds like it idles lower and sounds like crap, but while it's moving, it starts it's surging.

Also, when I started using the lawn mower again in 2013, I drained the old oil and refilled it a bit too much, and it always smoked on inclines.

It has a Briggs and stratton flathead motor. Any ideas? Could it be the ignition coil?