2004 dodge neon won't idle on start up?

Try retuning the engine. Luckily for an EFI engine this is as easy as disconecting the battery for a few minutes and then reconnecting. Start the car after retuning and see how it idles, hopefully it will fix the problem. Good luck! If the problem still remains, and when you give it some gas, it actually LOSES RPM, this may be a problem with the ECU/ECM, or a fuel problem (try draining a bit through the nipple on the fuel tube going into the injectors in the intake manifold).