Nope -- just plain ol' orbital mechanics. The operative principle is: "speed up to slow down, slow down to speed up."
When its orbit is closer to the sun than ours it goes faster, and catches up to us from behind. This speeds it up, and raises its orbit. Then we are behind it. When we catch up to it from behind, we pull back on it, slow it down, and its orbit drops below ours, and the cycle starts again. Pretty nifty business.