Idle Air Control (IAC) testing

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concretejungle

concretejungle

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The background is that everything was great with the rig and then i decided to bolt a TRD Supercharger up.

The only issue that i'm having is cold, first starts. The truck will fire right up, but then it just drops rpm all the way down and cuts off. If i hold the gas just a tad while starting it to give it throttle, then it will start and after about a minute, i can let off the gas and it will idle, low, but it will idle. Then, has the truck warms up, it idles perfect and starts perfect. That's it. Other then that the truck runs amazing and i'm loving the power.

First thing i did was to check all the routing of the vacuum lines. They all appear to be routed correctly and they are all brand new.

Which leads me to the IAC wiring. I had to cut and extend it. I felt like i did a good job, but maybe not. So i want to test it first before cutting all the tape and casing off it.

The FSM shows this procedure to test the circuit. My question is right there at the bottom "Condition: temp. at 20degreeC (68degreeF)"

Should i wait until the truck is completely cold, turn on the ignition only, then test the ohms? Or should i leave the ignition off considering it does not mention turning it on anywhere in the procedure.

IMG_2477.webp
 
Basically they are just saying to test at nominal room temp.

Obviously to measure the resistance you must UNPLUG the connector, which means at that point there's no power to the IAC anyway.... So, yes, ignition/engine off.

I'd also check the TPS while you're at it - it's just next to the IAC. Make sure the resistance is correct and that the 'switch' is working properly.

cheers,
george.
 
OK thanks George i'll check both.

I knew i needed to unplug the connector... i didn't know if by measuring resistance i needed to be sending a signal to it and see if it's lower then it should. That's why i thought maybe ignition on is the way to go.

Based on what's happening, would you venture to guess i'm heading in the right direction?
 
When you use a meter on the resistance range, IT generates a small voltage across the probe leads to make a current flow through the device under test. So, the meter provides that signal...

Given the IAC controls the idle by allowing air to bypass the throttle butterfly, it is possibly the source of your low idle. The problem is that there are so many sensors with these modern vehicles, that many things could be causing problems (unfortunately).

I had a TPS go south on me over a period of time and it caused a high idle condition (~1100rpm) and it would also throw a CEL every so often P0510. New TPS took care of it, no more CEL and normal idle.

Since this problem is new (I presume) after the S/C install, I'd make sure everything looks good in those areas, especially the throttle linkages etc since you've had to 'gyrate' them into a new position. Make sure all the cables move nicely and aren't binding. It's worth checking that the throttle is set properly given the new position the cables are now running.

Can't think of anything else at this point...

cheers,
george.
 
concretejungle said:
Which leads me to the IAC wiring. I had to cut and extend it. I felt like i did a good job, but maybe not. So i want to test it first before cutting all the tape and casing off it.
Click to expand...

Wait a minute.

Unless I'm missing something, the IAC valve test will tell you nothing about your wiring job; it only tests the valve itself.
 
CJF said:
Wait a minute.

Unless I'm missing something, the IAC valve test will tell you nothing about your wiring job; it only tests the valve itself.
Click to expand...

Correct, I presumed he wanted to verify the valve was operational.

As you say, if he wants to verify the actual re-wiring integrity, then the factory tests aren't going to prove his wiring is good.

cheers,
george.
 
hmmm the FSM says that the test i'm talking about, by sticking the ohm meter into the plug (in the wiring bundle, not on the IAC), will test the circuit. There is also a test to test the IAC itself.
 
If the picture you supplied above is the one for the IAC WIRING (not the valve...), then it would appear you can verify some level of continuity, but the possibility of cross wiring still exists (given all the 'good' values are the same)...

When I cut wiring to a connector to extend it, I prefer to make each cut at a different length/position. This makes it very hard to mess up what goes to what AND keeps the overall bundle smaller since all the heatshrink you add to each cut, doesn't all line up to the same overall place. Bit late if you didn't do that the first time around :)

cheers,
george.
 
I will post up the full picture when i get home. I feel pretty sure it was to test the wiring.
 
OK, here is a snapshot of the top and bottom of the page. From what i am gathering, the top of the page is showing how to check the wiring integrity. It even says to check the wiring harness for an open and short.

IMG_2478.webp


IMG_2479.webp
 
Nope, the top is the meter test for the IAC valve, NOT the wiring. It is to test the guts of the IAC from an electrical perspective.
The bottom is a functional test applying external power to the IAC valve to verify it isn't stuck/binding.

Neither is for the wiring....

On my Jeep, I've cleaned the IAC (gets gunked up over the years) with some solvent to free up the plunger.

cheers,
george.
 
well damn! How can i test the wiring job without just tearing it out and redoing it? I have a new throttle body gasket that i want to mount, so maybe i pull it off and check it.
 
There's no easy way to verify the wiring without buzzing all the way to the 'other' end of the harness to/from the IAC.

I would say your only option right now is to open up your handiwork and re-examine it - only you know how well you extended the wires AND whether you may have mixed any up.... Take some pics of your work and post it up for some constructive criticism or thumbs up.

Is the IAC the one with the broken clip on its connector or was it the TPS (as per your other thread)?

cheers,
george.
 
As you probably know, the IAC is a little motor. One way I found to check it is to tap on it when the idle is acting up. That way if the motor is weak or has a sticky spot in the inner workings, the vibration will knock it loose. This worked on my friends 80. He had a high idle problem and he had a CEL code. Sorry, but I don't remember the actual code.

Do you have a code? I would guess that the computer would throw a code if it didn't see a return signal from the IAC. I only know that the computer did set a code when I left the MAF sensor unplugged once. Someone here probably knows for sure about the IAC.
 
No code. Just an issue with the initial start-up... and like i said it's not that it won't start, it just won't idle at start. If i hold the gas, it will idle.
 
george_tlc said:
There's no easy way to verify the wiring without buzzing all the way to the 'other' end of the harness to/from the IAC.

I would say your only option right now is to open up your handiwork and re-examine it - only you know how well you extended the wires AND whether you may have mixed any up.... Take some pics of your work and post it up for some constructive criticism or thumbs up.

Is the IAC the one with the broken clip on its connector or was it the TPS (as per your other thread)?

cheers,
george.
Click to expand...


Honestly George, i'm not sure which one is which until i get back to the house and look at it.

My only worry is that i felt good about the connections. I took my time and i'm worried redoing it all, might result in the same thing. I hope not, i just wish i could verify it was the wiring.

IMG_2462.webp


IMG_2463.webp
 
I wonder if this has anything to do with it? The ends of the wires going into the plug are all frayed and look terrible.

IMG_2502.webp
 
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