My 1999 crown victoria has been dieing when at ideal somtimes has rough ideal, but runs good when im driving, and the ideal will go to normal if i put it in neutral at stops. and somedays it just runs fine. i replaced the pcv valve and sensor and the fuel pressure regulator but it didnt fix any thing. and the trouble code comes up p1409

P1409 is a fault code fo the stepper motor in the EGR-usually they get dirty from carbon and you need to remove the EGR and clean it with throttle body cleaner. This egr (exhaust gas recirculation) stepper motor code is best checked by physically having a look at the bottom of the egr stepper motor. When the vehicle engine has a lot of mileage, a carbon build up will occur at the pintle rod at the bottom of the motor and make the exhaust gas passage difficult causing the code. When removed, the carbon can be clean and pintle rod freed up so that it moves. Yours is stuck open, causing poor idle since it is introducing exhaust gas into the intake manifold during idle, which if operating properly it will not do at all.