How to test IAC
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How to test IAC
I have a '97 SOHC 4.0 that I have little time to diagnose & repair so I've posted here before, just didn't get around to all the fixin' up over summer....
Now I'm back into it again, how can I check the IAC valve?
I've done the tests in the haynes manual; resistance across the terminals is OK & no shorts from terminal to ground so, according to that it should be OK but I still get the IAC howl & fluctuating rpms.
I have access to a regulated 12v power supply; if I have the IAC on the bench and put 12v across the terminals I hear the soleniod engage but the rod (& diaphragm seal) doesn't move. In fact if I probe gently and try to move it against the return spring, it feels solid whether the juice is on or not.
Would this be a valid test? should it move when I power it up?
If it's frozen solid, how come I get the howl and fluctuating RPMs, surely it should be steady, either high or low if the valve isn't working?
Any and all help appreciated, I'm in the UK so no easy source of parts to swap or compare with, and if I have to buy a new one I'm gonna have to import it myself so I need to be sure that's the fault.
Now I'm back into it again, how can I check the IAC valve?
I've done the tests in the haynes manual; resistance across the terminals is OK & no shorts from terminal to ground so, according to that it should be OK but I still get the IAC howl & fluctuating rpms.
I have access to a regulated 12v power supply; if I have the IAC on the bench and put 12v across the terminals I hear the soleniod engage but the rod (& diaphragm seal) doesn't move. In fact if I probe gently and try to move it against the return spring, it feels solid whether the juice is on or not.
Would this be a valid test? should it move when I power it up?
If it's frozen solid, how come I get the howl and fluctuating RPMs, surely it should be steady, either high or low if the valve isn't working?
Any and all help appreciated, I'm in the UK so no easy source of parts to swap or compare with, and if I have to buy a new one I'm gonna have to import it myself so I need to be sure that's the fault.
Last edited by allan1010; Nov 24, 2005 at 05:23 PM.
Post Fiend
Joined: Jan 2002
Posts: 5,859
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From: USA
Do you have the pin layout for your IAC ? vpwr /signal/ref ???
if so did you measure the voltages at the connector?
Also there should be a large hole and a small hole in the surface of the IAC where it sits on the throttlebody are the plugged with carbon sludge? if so clean them out and try it again on the vehicle.
The Iac gets its voltage from the pcm based on throttle position sensor.
Its the Idle air control valve during Idle.
What were your symptoms before trying to test it??
Rich
if so did you measure the voltages at the connector?
Also there should be a large hole and a small hole in the surface of the IAC where it sits on the throttlebody are the plugged with carbon sludge? if so clean them out and try it again on the vehicle.
The Iac gets its voltage from the pcm based on throttle position sensor.
Its the Idle air control valve during Idle.
What were your symptoms before trying to test it??
Rich
Elder User
Joined: Jan 2004
Posts: 805
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From: Pauline, South Carolina
They can freeze in place from carbon build up and metal oxidation. They may freeze closed or partially open. If it's frozen, I have not been successful at cleaning it and making it work, I've always had to replace it.
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Thanks for the answers, guys.
I don't have the pin-out for the IAC but I have a Haynes (only not right here, right now) so I can probably find it. Didn't measure voltages at the connector.
Rich, "the surface of the IAC where it sits on the throttlebody"...do you mean what I would call the "mating face", where the figure-8 O-ring is? The two holes there seem to be the same size to me. IF there is a difference it is tiny.
But the inside of the IAC has been thoroughly cleaned with throttlebody cleaner. It's like a brand new unit to look at. No gunky deposits anywhere to be seen.
Symptoms before removing it were the famous "IAC howl" sound which came and went with a noticeable click noise from the IAC and the rpm's dropping or rising significantly at the same time. So, the engine would be idling then you'd hear the click and then the RPMs would drop ot the engine would stall out and you'd hear the howl sound, a few minutes later you'd hear another click, the howl would stop and the engine would idle like there was no problem.
It's just like the valve is trying to move slightly to adjust the idle but was sticking, and would suddenly go wide-open or closed-down as it unstuck itself amnd over-compensated.
But on the bench I can't see any movement at all when the solenoid clicks.
I tried a similar valve off of my buddy's Focus on the bench, just to see what they're supposed to do and his clicks open and closed with the solenoid.
I don't have the pin-out for the IAC but I have a Haynes (only not right here, right now) so I can probably find it. Didn't measure voltages at the connector.
Rich, "the surface of the IAC where it sits on the throttlebody"...do you mean what I would call the "mating face", where the figure-8 O-ring is? The two holes there seem to be the same size to me. IF there is a difference it is tiny.
But the inside of the IAC has been thoroughly cleaned with throttlebody cleaner. It's like a brand new unit to look at. No gunky deposits anywhere to be seen.
Symptoms before removing it were the famous "IAC howl" sound which came and went with a noticeable click noise from the IAC and the rpm's dropping or rising significantly at the same time. So, the engine would be idling then you'd hear the click and then the RPMs would drop ot the engine would stall out and you'd hear the howl sound, a few minutes later you'd hear another click, the howl would stop and the engine would idle like there was no problem.
It's just like the valve is trying to move slightly to adjust the idle but was sticking, and would suddenly go wide-open or closed-down as it unstuck itself amnd over-compensated.
But on the bench I can't see any movement at all when the solenoid clicks.
I tried a similar valve off of my buddy's Focus on the bench, just to see what they're supposed to do and his clicks open and closed with the solenoid.
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