It's been sitting there and was perfect before your vacation, but for you to be able to determine that there was a problem, you had to start the car right? A bad timing belt tensioner could lead to a timing belt skipping or tooth. I'm not saying that this is your situation but there's always that chance.
Hey Army, how are you SO sure his cats are gone? Even if he has what you call the "china cat" syndrome, don't you think it's important that he figures out why his car is running so rich that it overheated his cats? It would be a bttch to burn up new cats.