High RPM

[zzzlpr]

This 2003 Expedition 4.6 seems to have a problem with the IAC.
The RPM gets really high if you stab the throttle (around 2200 rpm) either at idle or while driving, which makes me compensate with the brake while driving and the mileage has been really bad, not to mention the hassle of driving this way.

This is what I did so far.
Replaced the IAC twice to no avail.
Completely cleaned the throttle body and intake (filter is new).
There are no vacuum leaks.

The key thing, if I disconnect the IAC the problem disappears, but obviously it generates a code that the IAC is not working.
I connected back and the problem comes back.
I find hard to believe that I had 3 IACs malfunctioning (original+ 2 replacements).

Any ideas will be greatly appreciated.

 

[bhamilton]

the '03 with the 4.6 has two different spec'd part#s for the IAC. I had the same problem that you did. Got one from carquest and it did exactly what you say. Returned that one and got one from Napa and it worked like a charm. It's possible you're replacing with the wrong part# IAC. Call the dealership and see if you can get the part# for the one that corresponds to your truck (you'll have to give VIN), then cross-reference that with the ones you're buying.

This is the one I got from Napa that worked: http://napaonline.com/Catalog/CatalogItemDetail.aspx?A=CRB216790_0193289980&An=599001+102003+50028+2028001&Ar=AND(P_RecType%3aA)

 

[zzzlpr]

Thanks, it does make sense that the part is not responding to the commands from the ECU correctly.
Perhaps the air passage is too big on the wrong part.
I bought the new IACs at Autozone.

I restricted the passage of air from the intake to the valve and the truck is working great, but I suspect that if there is a variation in the running conditions that requires the IAC to operate as intended I will have to deal with problems while idling.

Maybe my solution might work if the problem is the difference in size between the correct and the incorrect IAC, cause now with the restriction the volume of air is satisfactory.

Thanks again.