Testing the IAC with a noid light
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
Testing the IAC with a noid light
Okay, I'm going to show my ignorance here. Checking injectors with a noid light is obvious the way it works but what about testing the IAC? What is a normal behavior for a noid light on the IAC while the engine is running?
Instructor
Joined: Aug 2012
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From: Reno Nv
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Depends on what the engine is doing.
The easiest way to test an IAC with a noid light is to turn on the ignition key. The ECM recalibrates the IAC every time it's turned on (and turned off).
Basically you want to see both LEDs lighting up. It's not really important if they are red or green.
A noid light is a tester with LEDs that indicates that the wiring to either the injectors or IAC is working. You unplug the connector and plug in the noid light in place of what you're testing:
The easiest way to test an IAC with a noid light is to turn on the ignition key. The ECM recalibrates the IAC every time it's turned on (and turned off).
Basically you want to see both LEDs lighting up. It's not really important if they are red or green.
A noid light is a tester with LEDs that indicates that the wiring to either the injectors or IAC is working. You unplug the connector and plug in the noid light in place of what you're testing:
Last edited by Cliff Harris; Jun 5, 2013 at 12:31 AM.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Thanks Cliff, I have to partially disagree, it does matter if the leds are red or green. I believe color would indicate direction of travel which is my reason for using the noid in the first place. The iac is constantly changing directions with varying engine loads and I don't think mine is showing that kind of activity. I can start the engine and there may or may not be any changes to the lights. Sometimes I am getting both red and green from the same led while the other one is a steady color.
Race Director
Joined: Apr 2002
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From: Anaheim CA
The IAC is a stepper motor. It uses two square wave signals that are 90° out of phase with each other. The direction of the steps is determined by which signal leads the other.
My experience is that the IAC noid lights don't do a very good job of determining the phase of the signals, so the LEDs tend to do wacko things you wouldn't expect. I DO have one, so that's where my experience comes from.
Unfortunately my oscilloscope only has two channels so I can't record the IAC signal. The signals are not referenced to ground, so a four channel scope is needed with two channels in differential mode.
My experience is that the IAC noid lights don't do a very good job of determining the phase of the signals, so the LEDs tend to do wacko things you wouldn't expect. I DO have one, so that's where my experience comes from.
Unfortunately my oscilloscope only has two channels so I can't record the IAC signal. The signals are not referenced to ground, so a four channel scope is needed with two channels in differential mode.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
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From: WV
I used a scanner to check that my IAC was working correctly.. You can see it change as the rpms go up, and see it react when you turn on the key..I have an IAC readout on both my Autoxray 6000 and the Datamaster program on my laptop...
.....WW
.....WW
Last edited by WW7; Jun 6, 2013 at 07:11 AM.
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