Testing IAC
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Mountain Pass
Joined: Jun 2020
Posts: 111
Likes: 13
Testing IAC
I have a 1988 F250 5.8l that runs rough at idle. I thought it was the idle air control valve, which it still might be, but I want to verify the correct way to check it using a multimeter.
The orginal IAC reads 0 ohms when probing the two terminals. According to the below link and other sources, the IAC should read between 7 - 14 Ohms. Simple enough, mine read zero so it is bad. Went and purchased a new one, installed it, and the engine still idles rough. I checked the ohms on the new one and it reads 0 too. Thinking the new one was bad, I went and exchanged it. Got it home and it reads 0 too. Alright, so now the parts store gave me two faulty IAC's. I brought my multimeter to the parts store and checked two more IAC valves and all read 0 ohms. I walked out of the store feeling like a *******.
How do I properly check the IAC?
https://www.fullsizebronco.com/threads/how-to-clean-and-test-your-iac.206960/
The orginal IAC reads 0 ohms when probing the two terminals. According to the below link and other sources, the IAC should read between 7 - 14 Ohms. Simple enough, mine read zero so it is bad. Went and purchased a new one, installed it, and the engine still idles rough. I checked the ohms on the new one and it reads 0 too. Thinking the new one was bad, I went and exchanged it. Got it home and it reads 0 too. Alright, so now the parts store gave me two faulty IAC's. I brought my multimeter to the parts store and checked two more IAC valves and all read 0 ohms. I walked out of the store feeling like a *******.
How do I properly check the IAC?
https://www.fullsizebronco.com/threads/how-to-clean-and-test-your-iac.206960/
Thread Starter
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Mountain Pass
Joined: Jun 2020
Posts: 111
Likes: 13
Maybe test that the multimeter is functioning correctly on something else with a known resistance. Could be a faulty meter or bad test leads.
https://www.youtube.com/watch?v=38akaRKSY9c&t=57s
https://www.youtube.com/watch?v=38akaRKSY9c&t=57s
Thread Starter
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Mountain Pass
Joined: Jun 2020
Posts: 111
Likes: 13
Well it still has a rough idle. Just checked the new throttle positioning sensor to see if it is good and lo and behold it has no signal voltage when back probing the wire. Has 4.98v on the feed wire and 12v at ground. Guess I'll swap that out tomorrow for a different one. These aftermarket parts suck!
Cargo Master
Joined: Nov 2009
Posts: 2,190
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I don't really want to be an ***, but on IAC solenoids, specifically, none of the aftermarket units are worth a damn. It's completely believeable that you got four bad ones in a row.
That being said, since apparently it does need to be said (even though it shouldn't need to be said) go through your truck, and clean your grounds, before you break out the parts cannon.
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Mountain Pass
Joined: Jun 2020
Posts: 111
Likes: 13
Were they motorcraft IAC's, or Standard Motor Products/Echlin/cheap chineseium?
I don't really want to be an ***, but on IAC solenoids, specifically, none of the aftermarket units are worth a damn. It's completely believeable that you got four bad ones in a row.
That being said, since apparently it does need to be said (even though it shouldn't need to be said) go through your truck, and clean your grounds, before you break out the parts cannon.
I don't really want to be an ***, but on IAC solenoids, specifically, none of the aftermarket units are worth a damn. It's completely believeable that you got four bad ones in a row.
That being said, since apparently it does need to be said (even though it shouldn't need to be said) go through your truck, and clean your grounds, before you break out the parts cannon.
The engine has good throttle response and runs smooth when holding the throttle an 1/8th or so open. Comes idle time she isn't running that great.
Forgot to mention I've went through all the grounds I could find (5) and cleaned them all up two or three weeks back. Been searching for vacuum leaks but haven't found any yet.
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Cargo Master
Joined: Nov 2009
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I don't know what the non-motorcraft branded IAC's are doing differently, honestly, but they honestly are crap. I'm not even trying to be a fanboi here.
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Thread Starter
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Mountain Pass
Joined: Jun 2020
Posts: 111
Likes: 13
I wanted Motorcraft, but didn't wanna shell out the money. Now wishing I did considering my time removing the new unit and running back and forth to the parts store testing junk new parts cost more than $50.
Lead Driver
Joined: Jan 2019
Posts: 5,076
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From: N.W. Alabama
What rotten luck, also explains why our GURU's always say use Motorcraft, and test the new before installing, rolling snake eyes that many times explains why they tell us to check, clean check again....parts cannon...
Cargo Master
Joined: Nov 2009
Posts: 2,190
Likes: 620
Heh, I like to use Motorcraft where available, as you are generally going to get better parts, but I'm under no illusion that there's no good non-Motorcraft parts, I use em. It's just for some bloody reason, none of the aftermarket guys seem to be able to get the IAC solenoids right, and it's kind of always been this way
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