doubt it caused your problem, don't you have "N" on the selector?

Without turning the engine on, I put it in reverse (it's an automatic)>and rolled down the driveway a bit to... I really can't remember. It is>probably a REALLY stupid thing to do. Ever since then my car can barely>start (it acts like the idle is really low,) but adjusting the idle>doesn't seem to do anything. It works OK when moving, but once I stop,>the engine revvs really slow and sometimes almost stops; once I start>again, it goes really slow until I hear a "POP," like vapors igniting>in the exhaust, and then it accelerates. I am asking whether my car>running worse is a coincidence, or if I broke something really>expensive.