2004 Ford F-150 Emission Failture

With electronic throttle control or with out?
This code set when PCM detects an engine idle speed less than desired RPM
possible causes :
Air intake restriction
exhaust restriction
damaged throttle body
bad computer
IAC valve open
and so on there isnt a part that I would say remove and replace and problem solved
things need to be checked
1st we need to know if with or without electronic throttle body?

KE2 DTCS P0505, P0506, P0511, P1504 OR P1507: (OR STARTS ONLY AT PART THROTTLE) CHECK
THE VPWR VOLTAGE TO THE IAC VALVE

NOTE: If EGR DTC P0402 was output during the self-test, diagnose it first before continuing with this pinpoint test.
à   IAC Actuator connector disconnected.
à   Key in ON position.
à   Measure the voltage between:
( + ) IAC Actuator Connector, Harness Side ( - ) Vehicle Battery VPWR - Pin 1 Negative terminal
Is the voltage greater than 10.5 V?
Yes Key in OFF position GO to KE3.
No Key in OFF position. REPAIR the open circuit.

KE3 CHECK THE RESISTANCE OF IAC VALVE
à   IAC Actuator connector disconnected.
à   Measure the resistance between:

( + ) IAC Actuator Connector, Component Side IAC - Pin 2 VPWR - Pin 1 ( - ) IAC Actuator Connector, Component Side
Is the resistance between 6 ohms - 15 ohms?
Yes
GO to KE4.
No INSTALL a new IAC Valve.