another 4.0L high idle thread

[Stranger ranger]

So I'm still dealing with a high idle issue in my ranger. Threw on a new IAC, no fix. I checked for vacuum leaks the best I could, no prevail. I replaced the upper intake manifold gasket, still idles high at right around 2k rpm.
but get this,,,, When I unplug the IAC, the idle drops to 750-1100 warm, lower when cold, but my throttle response is horrible so I'd like to keep it plugged in. With my old IAC i could usually tap on it to get the idle to drop which is why i replaced it and with the new one, while plugged in, i tapped very lightly on it just to see what happens and nothing happens until i unplug it and it drops immediately.

Any takers??? This has really become a nuisance to me and it makes me look like some type of jack ass when I come to a stop light.

 

[BlackBII]

Is your throttle plate closing all the way?

I have had a few throttle cables that stick, causing the throttle to not close all the way...

Air has to be getting into the motor somehow...sounds like a leak somewhere. Every Ford I have owned, when unplugging the IAC, the motor will die, due to lack of air entering the motor. Yours staying at 750rpms makes it look like air is getting in somewhere else..

 

[Stranger ranger]

when i unplugged my old IAC it would do nothing so now that I know the IAC is sort of operating properly, I can move on to other things. I removed the cruise control unit because I read somewhere this was an issue for someone, but of course not mine. The throttle is not sticking so that's out. I might, MIGHT have a leak around my PCV valve so i'll look into that. What about a bad brake booster?

 

[Stranger ranger]

found it! cracked hose going from throttle body to the charcoal canister. Used propane torch to find.

On another note, why would my rpm go up when the brakes are applied? I figured they would go down since its pulling vacuum. complete opposite last night when i was bleeding my brakes.