I am also having this high idle problem on my 92 f150 with 5.0. Mine idles very high with the IAC plugged in and when I unplug it it idles where it should. I forked over the $75 for a new one installed it and it does the same thing. I am getting quite upset. I have checked everything I can think of. Hope someone can help one of us on this issue. What a pain in the butt.

 

ok I am getting mad now. sniffed around with a map gas torch (didnt have propane) no change in rpm put old IAC back on No the surgeing is gone but it seems to be unaffected plugged in or not. Turns out I had the TPS on 180 degrees wrong....... but guess what>>>>it doesnt matter cuz nothing changes. BAD TPS??? Well i bought a brand new one and did the voltage and ohms test and they match perfectly!! the only thing is is the resistance at closed idle is about 350 500 ohms as you open it it goes to about 1050 ohms and then infinate resistance. This is on both the brand new on and the one I have What the hell???? Any thoughts. What should the rpm be at idle running warm anyway??

 

Captain,

Had you replaced any parts prior to the IAC that might give us a clue?

 

had not replaced anything truck was running fine. only thing i did was give it a tune up new gas filter air filter plugs and wires and cap and rotor.

 

I had also replaced the cap rotor and fuel filter? Cant imagine that having anything to do with our problem.

 

and my vacuum canister (coffee can) had a hole rusted thru and i repaired it, I unhooked battery when i did the repairs and when i restarted the truck I thought i had it then I drove it and got it warmed up parked it and the idle gradually just went back up and when i unplug the IAC the rpm goes really low truck almost stalls out

 

mine is a 5 speed and I look like a real idiot driving it when i go thru the gears it just revs out. LOL

 

this is a pain know of any real good way to check for vacuum leaks. What is that contraption behind the intake manifold between the firewall that vacuum lines go to.

 

i have been just removing all my vacuum lines and using my Mighty Max vacuum pump on them. And did the same things with all the vac switches and canisters also. I have got to figure this thing out today. I got to start driving it! Its very frustrating! I will keep you posted on my progress.

 

that contraption is part of the air pump for the emissions. Cant remember proper name. I deleted that on my 89 mustang 5.0 and also deleted the entire smog pump and all the hook ups for it. It actually runs better and more power without it. Im thinking of doing the same on the f150

 

is it possible that the MAP sensor i pulled at the junkyard was for an automatic and causing issues with my manual and its computer??

 

Im at the point of taking everything back off including the TB and upper intake and just checking everything out again. Its been my experience that sometimes just doing it over can fix a problem as crazy as it sounds

 

its been my experiance that the map sensor is the same weather its a auto or 5 speed. at least on the older vehicles like ours. Im in the process of going thru everything again. if I dont find anything i think im going to change my throttle body and remove my plentum and clean it.

 

ok i ran codes again and now i have a code 41 which points to the 02 sensor. Did a search on the forum and learned that it could also indicate a coolant temp sensor fault?

 

tsarge I found my problem! the coffee can vacuum canister on the driver side fender had a tiny pin hole in it right where it sets in the holder. I took some fiberglass cloth and resin and covered it and it works fine idle is back down where it should be. Take your coffee can out and blow into it see if it holds air. you very well could have a pin hole in it. I thought mine was ok until I blew into it.