I suspect I may have a malfunctioning (failing?) idle air control valve. Every once in a while (I wish it were more consistent) I start the truck and it immediately dies... unless I hold the accelerator to maintain 1000 to 1500 rpm. Typically, as the engine warms up, the engine operates normally. Only once, the problem occurred with the engine at normal operating temperature. To remove the idle air control valve appears to be a very simple task (Only two screws from an easily accessible location.) I’m sure there’s a proper technique for checking it’s function to determine if it‘s okay, needs cleaned or needs replaced. I’d like to know how to test and if appropriate, clean to restore proper function. If it needs replaced , fine. I just don’t like throwing parts at a problem “just in case”. Especially $140 parts. Any advice would be appreciated.
Testing an idle air control valve
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Jwalker
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2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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It's a separate part on the 2000 5.3L. It may be built into the 2003 5.3L throttle body after the switch to drive-by-wire.
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OpalLacod,
I have been over the ground you describe.
I do have a cable throttle body.
The piece missing in your feedback is that I am driving a '03 Chevy Express 3500,
For some reason there is a hole across all sources for an IAC replacement.
The closest I have gotten is to trying to match engine and throttle body from a 2500.
With all that, is there a way to test an IAC, and would I be correct to qualify it as failed if the piston is fully extended?
I have been over the ground you describe.
I do have a cable throttle body.
The piece missing in your feedback is that I am driving a '03 Chevy Express 3500,
For some reason there is a hole across all sources for an IAC replacement.
The closest I have gotten is to trying to match engine and throttle body from a 2500.
With all that, is there a way to test an IAC, and would I be correct to qualify it as failed if the piston is fully extended?
2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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I went back to the OP vehicle description. Oops...
2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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Testing
I did not know this, but it makes sense... Apparently these valves are stepper motors. So, it should be "stuck" in place. If it's not "stuck", then the threads are stripped or something inside is broken. You can test the windings for resistance to make sure they are not shorted out inside. You'll need a proper pin-out for the IAC you have (or a similar one). All the GM ones appear to be very similar. If you want to play with function, find out which prongs are paired together and then apply 5V across them and run the IAC in and out.
![Image]()
TMI
I had already run down this rabbit hole before the testing question, so here's the rest of my train of thought.
2003 3500 Express Throttle Body has the same casting markings as...
![Image]()
2001 Silverado.
![Image]()
The only difference I can see is the part number on the butterfly. Everything else looks identical...
Idle Air Control Valves are all 4 pin (based on wiring for 2003 3500 Express and the IAC Valve shown in the 2001 3500 Silverado category).
![Image]()
![Image]()
I think you can get an IAC from another model 3500 and be OK.
I did not know this, but it makes sense... Apparently these valves are stepper motors. So, it should be "stuck" in place. If it's not "stuck", then the threads are stripped or something inside is broken. You can test the windings for resistance to make sure they are not shorted out inside. You'll need a proper pin-out for the IAC you have (or a similar one). All the GM ones appear to be very similar. If you want to play with function, find out which prongs are paired together and then apply 5V across them and run the IAC in and out.
TMI
I had already run down this rabbit hole before the testing question, so here's the rest of my train of thought.
2003 3500 Express Throttle Body has the same casting markings as...
2001 Silverado.
The only difference I can see is the part number on the butterfly. Everything else looks identical...
Idle Air Control Valves are all 4 pin (based on wiring for 2003 3500 Express and the IAC Valve shown in the 2001 3500 Silverado category).
I think you can get an IAC from another model 3500 and be OK.
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quote:
Testing
I did not know this, but it makes sense... Apparently these valves are stepper motors. So, it should be "stuck" in place. If it's not "stuck", then the threads are stripped or something inside is broken. You can test the windings for resistance to make sure they are not shorted out inside. You'll need a proper pin-out for the IAC you have (or a similar one). All the GM ones appear to be very similar. If you want to play with function, find out which prongs are paired together and then apply 5V across them and run the IAC in and out.
end quote
I have done a continuity test across the two circuits and they are both 4.3 (+/-) Ohm.
All the new IAC valves I see and one replacement video show the new IAC piston to be retracted. In the video the failed one is extended. Since my issue is the van is not idling correctly at start-up, I imagine the piston is closing the bypass air passage. BUT once warmed up the engine idles normally. So by that, I assume one of the IAC HIgh Low circuits is working (?).
Testing
I did not know this, but it makes sense... Apparently these valves are stepper motors. So, it should be "stuck" in place. If it's not "stuck", then the threads are stripped or something inside is broken. You can test the windings for resistance to make sure they are not shorted out inside. You'll need a proper pin-out for the IAC you have (or a similar one). All the GM ones appear to be very similar. If you want to play with function, find out which prongs are paired together and then apply 5V across them and run the IAC in and out.
end quote
I have done a continuity test across the two circuits and they are both 4.3 (+/-) Ohm.
All the new IAC valves I see and one replacement video show the new IAC piston to be retracted. In the video the failed one is extended. Since my issue is the van is not idling correctly at start-up, I imagine the piston is closing the bypass air passage. BUT once warmed up the engine idles normally. So by that, I assume one of the IAC HIgh Low circuits is working (?).
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You mentioned in a previous post to use a 5v source.
How did you come up with 5v as an operating voltage?
I read one post where someone tried this with 12v and cooked the IAC.
2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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I was reading a troubleshooting guide and how to test it with a multimeter "looking for ranges from 0V to 5V" from the computer. I believe the TPS uses a 5V reference voltage, so it seemed reasonable. You can probe the IACV plug with a multimeter to verify max voltage the system pushes to the IACV.
We should be able to find a spec sheet on one of these widgets...
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Sounds as if my 4.3 Ohms is a partial burnout.
If I tasked you, what IAC would you find to put in the pull cable throttle body of a 2500 w/ a LQ4 (6.0L LS)?
2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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I'll do some digging when I get back on the computer. Got distracted by the broken spider gears I found yesterday...
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I have been comparing throttle bodies and find:
Cardone 671075
which looks the same as Cardone 671014 except the Cardone 671075 has a vacuum hose attachment built-in.
Note how black lines have been painted on the butterfly sides ... to make it look different?
My Throttle Body looks like the Cardone 671014, but has a vacuum hose just behind where the Cardone 671075s is located.
The intake ports are the same.
So, did Chevy pull some intake manifold out of its ass to get the 2003 6.0L LQ4 on the market?
What I have not found yet is why the Cardone 671075 and Cardone 671014 do not come up with, or I haven't found, the same IACs. The one manufacturer I found that does both has a IAC47 and IAC33. Between the two I only note a offset in the female connector, same as the CV10017 and CV10011.
So the only difference I can imagine is in the electrical circuits and/or wiring from the PCM(?). I have inquires out but am not hopeful.
2000 Silverado Z71 4x4 5.3L 490k+ miles w/ GM rebuilt motor and trans
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The unit you show on your truck has the same butterly stamp as the CARDONE 641075. This is the same unit as shows for buying a new throttle body and putting it on my truck (2000 Silverado 5.3L). Your intake manifold also has the same vacuum line setup as my truck...
What is the part number for your ECM? If it's a similar model to any of the other trucks out there, I'd be willing to bet the pinout is the same...
What is the part number for your ECM? If it's a similar model to any of the other trucks out there, I'd be willing to bet the pinout is the same...
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We are getting close ...
RockAuto does not have a throttle body for your 2000 Silverado 5.3L. = : /
I will have to dig for the ECM and while we are at it, previous references have been to a PCM.
I assumed that a PCM was what I understood to be an ECM. Are they different?
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