Report: PO171-174 Engine codes
Ford F-150 Problem
Model Year Affected: 2004
Check engine light with PO 171-174 codes with the 5.4 motor.
PCV elbow is leaking vacuum at the connection at the back of the throttle body by the firewall.
The vacuum elbow has to be replaced and is available from Ford either with the entire PCV line or just the elbow.
make sure you remove the battery cable for 30 seconds after the repair to clear the adaptive memories.