check your intake plenum for a leak. it may be hard to find but if you use a can of carb cleaner and spary it down it will idle up if there is a leak. sometimes you need to use a scan tool with an o2 sensor graph to find it. but the plenum tends to be a common place for leaks.
2005 Ford F-150 STX, 4.6L V8, K&N CAI, Magnaflow 2.5" dual rear exhaust, custom dual 16" E-fans, 6000K HID headlights and foglights, tinted tail lights, painted badges.
2005 Honda VTX 1800R with cobra exhaust.