Hi I have a 2004 f150 lightning, my problem is that I have low idle around 750 rpm in park then when selecting drive or reverse it drops to under 500 rpm it feels like its going to stall. And also my gears won't change right , when I pull off it stays in 1st gear unless I let off the acceleration then it changes into 2nd and also traveling at 30 mph with around 1500 rpm it constantly changes from one gear to another.
I have been to 3 different garages with the problem and had three different answers 1. New transmission 2. New ecu 3. New fuel pump

 

Any OBD2 codes?

 

No I have no codes at all

 

For the low RPM problem, pull off your IAC and take some sea foam deep creep and clean it out. If you disconnect it while running the truck (when operating properly) it will go low like you are saying.

AFAIK it will only throw a code when not connected.