on my 1990 f-250 4x4 with the 5.8 . when the truck is idleing and the IAC is connected the RPM's surges up and down . and when i hit the accelerator it takes forever to come back to a idle . but ,when i unplug the IAC it stops surging and when i hit the accelerator it goes up then right back down like it is suppose to . i OHM'd the IAC and it says it is suppose to be between 7 and 13 to be good , mine is 9.4 . the IAC shows good so what is wrong ? already put on a new TPS the old one was bad .

 

Whenever I unplugged my IAC, the motor dies at idle. I think yours is sticky/stuck.

Pull it off, you should be able to move the valve portion with a small screwdriver. You can removed the actuator also(two small screws). The actuator should move easily. If it sticks, it's bad. Clean it up with brake clean, make sure valve portion is cleaned out. Reinstall and try again.

I bought a new one at Azone and it was junk. Had all kinds of driving issues as it would take forever to come to idle after letting off throttle. Kinda hard to drive when it would try to keep going!!! PITA POS. I cleaned the old one up and put it back on. Much better!!! Drives normal now.

 

thanks , i will give it a shot .

 

+1 to freight train. What brand is it? Any marking?

Use that or throttle body cleaner and spray through. Paper towels until it's shiny. You should be able to hear the valve when you shake it. Your hunt at idle is it jerking back and forth because it's sticking. Same thing causes it to hang up before dropping into an idle speed.

What kind of MPG's are you getting? Since the truck is running with it disconnected, seems like your comp has adjusted it's maps to compensate for this problem. Once you clean it you'll need to drive awhile or disconnect the battery for an hour to reset the computer. If you go the battery route it'll run rough for a few minutes then you should be good to go.

 

no MPG's yet . i just wanted to clarify and fix the problem before i got it going again . i just got done getting the motor re-built and got it sitting back in the truck and was hooking everything back up . it had this problem before i pulled the motor. the reason for no MPG yet is i just bought the truck and aint got to drive it much before i pulled the motor.

 

+1 to all this. I had an IAC valve go bad on an 89 T-Bird we used to have. I put on a 'new' one from the local parts store, but the problem didn't go away. Stumped, I gave up and took it to the local dealership to let them have at it. The result? Bad IAC valve. Turns out the new one was junk. Lesson learned; only OEM for these kinds of things.

Mike

 

yeah i didnt answer dave804's question . it does not have a name or I.D. on it that i can see . and yes i agree also OEM parts is a plus .