89 bronco II idling/running rough

[Little Grass]

I feel like im chasing a ghost. I recently started trying to fix it up and get it running right. Its throwing the code "54" but i have replaced the AIT sensor and the AIT connector. It has new injectors, new fuel pressure regulator and alternator. It runs like a champ after 2k rpms but below that it just sounds rough and idles around 500 rpms. Im lost as to where to go next. It will only throw the code "54". Any assistance is GREATLY appreciated.

 

[tw205]

I wouldn't depend on a new AIT being a good AIT. Have you disconnected it while running? Ohms test the sensor when at room temp then heat it with a hair dryer or heat gun and check resistance again. Should change, if not, bad sensor. How's the timing? Spout plugged in?