Yes, replacing the IAC cleared up my problems. I replaced the OEM IAC with a BWD one from Advance Auto back about 07, so far its been fine.

If you decide to replace yours, if you buy online with discount codes like these http://www.retailmenot.com/view/adva....com?c=5055807 & opt for in store pickup to save shipping charges, you can save a considerable chunk of your gold!!!!!

 

Well the saga continues.... just installed a new IAC and truck fires up at 2000 rpm..... now what?

 

Well 2K rpm on a cold start is about right. If it stays there after its warmed up, did you perform the cold & warm idle relearn procedure after the battery B- cable disconnect, as that'll wipe the old corrupt idle & fuel trim tables, so it'll want to relearn its cold & warm idle strategy & begin to build new fuel trim tables.

If you've already done that, then look for a vacuum leak down stream of the MAF sensor & include the PCV valve & its rubber hoses & grommet in your search, or maybe a dirty slightly stuck open throttle plate & let us know how it goes.

 

The Saga goes on!!!
Well, I bought a new aic and all was fine for a over a weak... same problem again. Here is the real kicker!.... when my ac is on, the truck idles perfectly.... now this old mechanic is as lost as dorthy was in oz.

 

OK, when replacing the IAC, did you have the battery B- cable disconnected & if so, did you perform the cold & warm idle relearn procedure listed here Ford Truck Enthusiasts Forums - View Single Post - high idle problem

Disconnecting the B- cable wipes any trouble codes, the idle strategy & fuel trim tables stored in the KAM & clues the computer that a repair has been made, so that it'll begin rebuilding new fuel trim tables & relearning its cold & warm idle strategy, but we may have some driveability problems. The idle relearn procedure may help it get started & avoid driveability problems. I take the time to do it after a battery disconnect.

Have you looked for any vacuum leaks that might be downstream of the MAF sensor, like the PCV valve its hoses, intake manifold gasket, ect. Or have you connected a scantool to have a look for pending, or stored trouble codes & have a look at both cyl banks fuel trim????

Seeing as how the idle will improve when the AC is on, suggests that the IAC itself & wiring to it is functional.

Has the throttle plate idle screw ever been messed with, or has the throttle linkage or throttle plate been disconnected, or repaired, before the closed throttle idle anomaly began????