Got your PM. The knock sensors monitor combustion in the chambers, and guide the DME in retarding or advancing ignition spark. If one is faulty, you'd get pretty much the symptoms you're describing, although I'm not sure if it would include the smell of gas. You may get lucky and find that the wiring harness to #2 somehow got unplugged. Or more likely, it has to be replaced, which is about $75 for the part, I don't know how much labor will cost.
Hope this helps!