I am not sure if this is in the right forum, if not I apologize. I have a 97 F150 4.6L (VIN 6) 4X2 reg cab. When the engine is warm I have a rough idle issue while the truck is in gear, like when stopped at a red light. I also have very poor gas mileage. I did have a P0401 code, which I no longer have. I have replaced the EGR, DPFE sensor, ignition coils, new plugs and wires and have changed the fuel filter. What am I missing?

 

Update: The check engine light came back on, code P0401. Didn't want to, but bought new EGR valve from Ford and installed it. Code went away for two days and light came back on, P0401. My mechanic said he checked the throttle body and it didn't seem to be clogged. He also did not hear and leaks from the engine. I have no idea what is going on with this thing, but it's very annoying!

 

I know it's probably unlikely, but your timing could be off a few degrees. Be sure to disconnect the SPOUT and check the timing when it is warm and idling rough.