I had this problem randomly one night on my '06 G6 4cyl, i ran codes, looked for parts, bought a few parts, was out a car for a week and i decided to take one last look at it and the clasp holding in the throttle position sensor had broken and the sensor came out. It was wedged between a flat aluminum tube and the VVT (Cylinder Heads? [Sorry, still learning]) and i literally just had to push it back in. It sounded like death and thats all it took. So hopefully one of your sensors have come loose and thats all it is. I'd take a good look at all them to be safe, and diligently too, i wouldnt of seen the TPS if it weren't for the bright orange gasket.
When this happened to my 07 2.4, I replaced the spark plugs and the coil/boot for cylinder 2. This didn't fix it however. Ended up having to get a new cat and that solved the misfire, but I would also check your injectors or fuel rail as I did as well to make sure there weren't apparent fuel issues. Good luck!