Continue to ignore the IAC and everything will be fine

 

And you were thanked 124 times?

 

I replaced the IAC, didn't work. Does that narrow it down to the throtle position sensor?
Linkage is good, no apparent vacuum leaks. The truck is only drivable when I disconnect the IAC.

 

How about the pcv and tube that goes back around the engine? They leak at the elbow and could cause I high idle.

Here is some information for testing your tps: http://easyautodiagnostics.com/ford_...nose_tps_1.php

 

Take a look also at the fuel pressure regulator. check the vacuum line to the regulator. disconnect the vacuum line and you should see a significant difference in the idle of your engine if regulator working properly.

 

I disconnected the red vaccum line to the fuel regulator, no real difference in the idle. Maybe very slight but not significant.

 

I tested the fuel pump pressure at the regulator.
36psi. Key on not running
31psi running
40 psi running, vacuum line disconnected from regulator.

 

Fixed!
High idle problem fixed, it was the tps throttle position sensor.
Thanks to all who helped.

 

I'm not sure that's even possible, as it doesn't control or effect.

Glad it's fixed though.

 

jbrew
I replaced the iac,
checked all the vacuum lines
checked throttle linkage
checked fuel pump and regulator
all the above didn't change the high idle
I replaced the tps and immediately the problem is fixed, idles great.