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How to test an IAC valve/motor

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How to test an IAC valve/motor

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Old 06-18-2019, 09:29 AM
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Thumbs up How to test an IAC valve/motor

I am wondering if there is a procedure to test the IAC in my 2004 Ram 1500 SLT 4x4 w/ 5 speed MT. 4.7L V8

How can I tell if the part is working correctly? If I disconnect the connector and start the truck and keep my foot off the accelerator then it stalls within 5 seconds.
Which I assume is correct since I would assume when you shut the truck off the PCM tells the IAC to close to STOP all air into TB to shut off.
Then if I disconnect connector the last position of IAC is closed hence starts but stalls due to no air.

If disconnected and I give it throttle it does run.

Might be an academic question but it is the PCM that controls the IAC? Correct? I assume its based off of readings from the TPS & MAP perhaps?

So if anyone knows of a way to test the IAC to say if its good or bad I would much appreciate it.
Thanks
Kevin
 
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Old 06-18-2019, 09:38 AM
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Question becomes, what makes you question if your IAC is working properly?

All the IAC is, is a controlled vacuum leak. Only active at idle. (closed throttle.) It is indeed controlled by the PCM, which merely positions it to maintain what the PCM thinks is 'proper' idle speed. If your engine rpm flares to around 1500 at startup, and then slowly settles down to around 800 when cold, 650 or so when fully warmed, the IAC is working.
 
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Old 06-18-2019, 09:55 AM
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Yes thats the exact reason - still chasing my high idle. Goes to 1500 rpms and stays there. This is the only part I have no real clue on how to test.
TPS I was able to see voltage change and even remove and make sure ohms went up & down. Same with MAP, was able to put a vacuum pump on that
and test but I have no clue on how to determine if IAC is good or bad with multimeter or some type of simple test.

So I have no idea if my IAC is bad (stuck and not closing) or the PCM is telling it to stay open.
 
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Old 06-18-2019, 10:18 AM
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If you have a scanner, you can look at IAC "counts", and "Target Idle". See what those look like. (I would also be tempted to see what the PCM thinks TPS, and coolant temp are.) However, if the idle speed doesn't change at all, regardless of engine temp, etc, I would highly suspect a failed IAC.... Usually though, if the PCM can't control idle speed, it will whine about it. Don't know what exact conditions need to be in place, but, I am thinkin' that idling at 1500, on a fully warm engine, the PCM should NOT see that as 'desirable'...... You could pull the IAC out, (ignition off) stick it in something to restrict it's travel, (and avoid launching the pintle like a little friggin' missile, never to be seen again......) see if the PCM can actually control it. (A high zoot scanner would also let you manually control idle....... but, those are NOT cheap.)
 
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Old 06-18-2019, 11:12 AM
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I do have the highest level scanner that harbor freight sells the Zurich ZR13 but it doesnt have the ability to show IAC counts or target idle unfortunately.
The ECT seems to be reported correctly on the Live data scanner feed as well as the TPS. At idle TPS is about 11% - while driving it ranges from 11% at closed throttle to about 75% at wide open.
Yes 1500 rpms no matter what even when fully warmed +/- 200 rpms at times
And yes no codes at idle and warm. I can set a P0068 code when I try and keep the truck in gear for as long as possible to the point where it shakes and almost stalls to avoid the rpms going up to 3000 when scoming to a stop and I shift into neutral and the truck is still rolling. Usually it comes back down to 1500 when the truck has stopped moving.
So I dont know if this is a real code or not or my trying to drive the truck incorrectly to avoid an even higher idle is throwing off the PCM.

Do you know what the voltages should be at the IAC connector as sent from the PCM? I imagine it could be anything as Ive read it could have 256 positions of the pintle?
The IAC black plastic circle inside the valve moves freely in and out and I cannot blow any air through it with my mouth if that helps at all. I really dont know what im doing so I am trying anything to see if I can determine if its bad. Hadnt thought about removing it from TB and trying to hold back the pintle, sounds like safety glasses would be required!!!
 
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Old 06-19-2019, 07:18 AM
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Four wires on IAC connector, with engine off, key on, two wires should have 12 volts, the other two should go to ground. (this locks the IAC in place.) PCM will 'bounce' power to the IAC in order to move it in steps. Of course, it cycles that a LOT faster than any meter will be able to show you...... If the IAC can fully close, and completely block off air flow, then you have to have a leak somewhere. If you can't find an external leak, then it's likely an internal leak..... What is manifold vacuum at "idle"? Also, disable the PCV system, and see if you still have vacuum on the crankcase.
 
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Old Yesterday, 09:42 PM
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Sorry so long for a reply but I ended up getting rear ended in rush hour traffic and then my clutch slave unit finally did fail so I had to replace it as it was virtually impossible to shift the truck!
So my IAC only has 2 wires that measured 10 ohms that is the winding of the IAC motor.
My vacuum at idle was 19.5 which I think is where its supposed to be.
Not sure what you mean by disabling the PCV system. My PCV valve is on my oil fill tube. Do you mean to disconnect the PCV line and see if it sucks my finger?
My IAC definitely moves because when I shut the truck off and the remove the IAC connector and try and start the truck, it will start but then die after 5 seconds as the truck is starved of air. But connected it idles high, so I know on startup the PCM is telling it to open. Not sure what is supposed to happen after that. Seems like PCM should tell it to keep stepping down as truck warms up but have no way of testing that.
If I had an internal leak would the truck die like it does with my IAC connector removed? To me it seems like the truck is leak free as far as the manifold vacuum is concerned.
Can an EGR issue cause the high idle?
Could my PCM be shot? I mean it seems to be able to close the IAC and then open the IAC but Im not sure if it can control the IAC other than fully open or fully closed
and I have no clue on how to test that as I dont have a bidirectional can tool.
 
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Old Today, 07:38 AM
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Idle vacuum is good.

Yeah, disable PCV. Disconnect hoses, plug any holes. See what ya get.

Have you tired resetting the PCM? Disconnect battery, turn on headlights, count to five..... turn off headlights, reconnect battery, turn key to "run" (not start) count to ten, (don't touch anything) THEN start the engine.... Should force the PCM to reset all of it's 'zero' values for various sensors, and re-learn idle......
 

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