Ford Repair: 2000 f-250 wont idle by itself, air control valve, vacuum leak

Question
Hi i have a 2000 f-250 with a 5.4 in it it just started not idling by itself when you started it.   Sometimes after it has been run for awhile it will idle by itself but that only lasts if you dont leave it parked more than 5 minutes.   I have put new plugs in it changed the fuel filter and that did not work.   The other day i took it to the shop and had it put on the scanner and no codes came up.   The shop also tested the fuel pump and said it was week so i bought a new one and installed it.   That did not work so i turned up the idle on it and it idles a little better now but when you go down the road with it it runs rough and shakes.    Any suggestions.

Answer
Hello jrs, The idle is a idle air control valve or a vacuum leak, check the PCV hose fot a split. The runs rough is probaly a coil causing a ignition miss. I hope you didnt turn the screw in the throttle body ? If you did even after you correct what is causing your idle concern it still will not idle correctly, the computer controls that and is preset once it is turned the computer will "hunt" for the idle. You'll probaly have to replace the throttle body to correct it along with repairing your main concern to begin with. A dealer can do a Mode 6 data when the engine is missing out to see what cyl it is. Most times the IAC will not store a code. Hope this helps Thanks Tony