if you're getting a code get it read...its really the easiest way to narrow things down. someone on here said autozone reads them for free. guessing games suck. sounds like a sensor or maybe egr or something. its probably the throttle position sensor or idle air control valve.
and putting in injector cleaner can hurt, usually ends up clogging them up more than cleaning them out..there are a couple brands out there that are good, but you shouldnt have any injector clogs if you use a decent gas co. ..the detergents they put in cheaper gas suck for injectors.