1992 f150 super 4x4 with 5.8. when i first start it it i have to pump the gas right after to keep it running, then it idles really rough and surgy like. and then sometimes it will die. when i was changing the plugs yesterday i noticed the IAC was unplugged, so i plug it back in and the idle smooths out but idles at 1500 and won't come down, i unplug it, cel comes on and idle gets rough, how do you clean these and could that be the cause of the rough idle?

 

Unpluged, the IAC is closed and only the throttle stop is allowing some air thru.
Plugged up, the IAC is opening up and letting a lot of air in.
Plug the IAC up and start the motor.
Let it fully warm up, then evaluate if there might be a problem because the IAC is not stuck if it works to that extent but not a bad idea to take it off and spray clean with throttle body cleaner as well as the throttle body.
To clean the IAC spray inside and move the pintel to be sure is has operating range and that it's internal spring is still closing it.
Hold the throttle open and spray all around inside to remove sludge from the plate area that would interfere with airflow.
After all is back togather, remove one battery cable for several minutes so the computer will reboot.
Re install the cable, start the motor, turn the lights on hi beam, heater fan on hi and let warm up.
Do a drive cycle of at least 5 miles and several restarts.
This will cover most of the idle relearn and result in a good cold starting and hot idle assuming there are no other faults.

 

ok, i guess that the one i have can't be cleaned, i did try anyways and cleaned throttle body out with cleaner and spray contact cleaner on the connector, still idles rough and runs sluggish at low RPMS, i changed plugs, wires, cap and rotor and changed oil, and air filter. i don't know what else to look for? any ideas?

 

https://www.f150online.com/forums/sh...ight=high+idle


sounds like my problem. Changing the fuel filter fixed my abnormally high idle and code P0175 rich bank 2

 

well i tried to clean the TB and the IAC, nothing happened. still runs high and when i'm at a light it surges real bad and when i put in park it goes up to almost 2k. Took it to a shop with ASE mechanics,(though i'm doubtful) they said they would hook it up to the laptop. Calls and tells me the laptop don't power up with my PCM, i inform them it's not the original engine. But the PCM is for that engine, as the mechanic that did the change over got codes from it all the time. and the check engine light does come one. but goes off after i plug the IAC back up...but still runs bad. One thing they noticed was the EGR valve had no vacuum to it, and where we think the line should be coming from is capped off? Its a 5.8L, is that normal? and can anyone think of anything else i should try. the IAC don't look bad, looks pretty clean, not sure if i should fork out the 100 bucks for a new one. But i can't get a code to tell me. Don't know if ford could get the code. Any help would be great

 

What happened when you removed the IAC plug with the motor running?
Did the idle come down or did it stay high?
This is important to tell what's happening with the IAC.

 

yes when the IAC is plugged in it idles 1500-1800rpm eventually coming down to 1100 when fully warm, but when driving it surges, if i unplug it the idle comes down to about 700-750 and the CEL comes on.

 

My guess is you have a vacuum leak. Plenum base is wkere I would look for it. Seen it like that before. might need a new gasket there. Shoot propane around it while at an idle.

 

The importance of this is it tells you that the problem is not with the IAC.
A bad air leak it causing the high idle and that is changes with heat expansion of the leak area.
Bolts loose at the throttle body, bolts lose anywhere on the intake system, gaskets bad etec. Should not be to difficult to run this down.
Once you correct the fault, reboot the PCM and do the load re-learning procedure to get back to normal operation.

 

here is another odd piece, the egr valve has no vacuum hooked up to it, and there is a vacuum cluster at the top of the engine and the one that i would assume is for the EGR is capped off. So if its not the IAC, where do i begin looking for vacuum leaks at? is there an easy way to look? How do you reboot the PCM? just unhook battery? Thanks for the great help thus far

 

one way of finding leaks is to use propane one of those cheap torches go around things shooting it at areas if the engine starts to die you know you have a leak there. Yes just disconnect the battery for several minutes and that will reboot it. you can also use cab cleaner to find vacuum leaks spray it around if the engine starts to run rough thats the leak..

 

ill try that tomorrow and let you know if i find anything. Do you think the fact that the EGR Valve doesn't have vacuum hooked up could be causing issues. Where would be some common leaks to start at?