The at or above $450 limit may only qualify if done at an accreditted facility, by an accreditted technician but I'd have to brush up in that regard to be sure.

If the idle is at ~1000 RPM and is hunting 100 RPM or more consistently, then you have to perform all the basics to set timing, Idle Stop Switch, TPS, Boost leaks, and yes you could have a leaking injector which could be found somewhat by turning off the injectors with a logger but makes it more complicated if you aren't on the rollers. Without a consistent idle, elevated RPM and obviously bad tailpipe emissions are some issues that you can have.