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Old 05-20-2015
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Diagnose bad IAC valve?

Is there a procedure to diagnose a bad IAC valve?
I found a webpage that gave a range of resistance that is within acceptable by metering the terminals, and I'm on the lower end, but not at the bottom of the range.
I'm having a hard start or crank/no start thing happening with my 01 b3000.
when it starts, it idles down to stall unless I keep my foot in it, and even then not consistently.
I've got spark, fuel pressure is perfect; so it must be air/compression, right? any other ideas, if it's not the IAC? (I just cleaned it, along with the throttle body)

Help! I'm not ready to retire the old boy yet: 250k miles is nicely broken in.
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Old 05-20-2015
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Take the IAC valve off so you can see the valve.
Connect its wires
Turn key on, valve should open all the way
Remove wires, valve should close all the way

When you turn on the key with fuel injected engines, the IAC valve opens all the way for starting, that's why when engine starts RPMs go up to 1,500+ normally, then computer starts closing IAC to set cold idle, 1,100, or warm idle 700
This is not a Ford thing, all fuel injected engines use an IAC Valve and are programmed similar to this.

IAC Valves use Step or Stepper Motors, these can be turned to a specific "step", there are over 100 "steps" the computer can call up, so computer might call up "step" 100 to open valve all the way, and "step" 30 for warm idle.
This "step" part could fail, so OHMs are correct for an electric motor but "steps" are not working

Last edited by RonD; 05-20-2015 at 08:57 PM.
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Old 05-20-2015
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thank you once again, sir!!

Are those correct idle numbers for a 3.0 with manual transmission? I thought they were a bit lower...600-650 for warm idle. Or am I mistaken that there's a difference between manual and auto idle speeds?
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Old 05-20-2015
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Thats just an average
600-650 manual
700-750 auto

my manual idles at 623, lol
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Old 05-21-2015
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And that's WITH the AC running, those ranges, no? (which is pretty much any time the airflow controls are out of the OFF position as I understand it...)
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Old 10-12-2017
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Sorry to dig this up again, just wanting a double check on the 3.0 Vulcan hot idle, i saw someone mention (might be you, RonD) that said the Vulcan engine idle is higher than most V6's?

Got to check with a scanner, but the tach suggests it's idling maybe 800-900.

Coming to a stop (manual trans with clutch in) the idle speed is maybe 1500 until i come to 1mph or stop, then it lowers and dips low enough to sometimes cause the oil gauge to flick down before recovering.
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