IAC wiring puzzle
04-08-2003, 12:08 AM
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IAC wiring puzzle
I have posted about my IAC before, but now I have some more information.
My TB is a Holley 4 barrel unit with integrated IAC.
When I connect the diagnostic pin to ground, the IAC extends, and keeps trying to extend for quite a while. It seems to try to extend for a while, then it stops then it tries to extend for a while . . . . I say "tries to extend" because I have the IAC removed from the TB when I do this, and am holding it near a hard surface so it can't extend too far. So far, so good, I think.
When the engine is running and warmed up, eventually, the IAC counts will go to zero. When that happens, I can still hear the whistle of the air going through the IAC port, and my car idles at around 1300-1500 RPM. So, I stick my finger over the hole. This brings the idle down to 600-700. The IAC count starts to climb as you would expect it to. Eventually, when it gets up around 100 or so, if I remove my finger, there is very little flow through the IAC port. The IAC has extended as the count has increased. That doesnt seem quite right
What am I missing? Do I need to reverse the polarity of the two coils (or one of them) to get the thing to go the other direction? It has been a while since I mucked with stepper motors. I've checked the IAC and wiring with an ohm meter to verify that the two coils are connected to the ECM "correctly" but that doesn't mean the polarity is right. Might be trial and error time there are no coil polarity markings on the IAC.
Also, I read in one of the papers on the internet that when the engine is turned off, the IAC first resets, then extends all the way, then retracts 145 counts. When I turn off my engine, the IAC doesn't do anything. I do have constant power (orange wires) and switched power (pink wires) to the ECM, so I have that right.
My TB is a Holley 4 barrel unit with integrated IAC.
When I connect the diagnostic pin to ground, the IAC extends, and keeps trying to extend for quite a while. It seems to try to extend for a while, then it stops then it tries to extend for a while . . . . I say "tries to extend" because I have the IAC removed from the TB when I do this, and am holding it near a hard surface so it can't extend too far. So far, so good, I think.
When the engine is running and warmed up, eventually, the IAC counts will go to zero. When that happens, I can still hear the whistle of the air going through the IAC port, and my car idles at around 1300-1500 RPM. So, I stick my finger over the hole. This brings the idle down to 600-700. The IAC count starts to climb as you would expect it to. Eventually, when it gets up around 100 or so, if I remove my finger, there is very little flow through the IAC port. The IAC has extended as the count has increased. That doesnt seem quite right
What am I missing? Do I need to reverse the polarity of the two coils (or one of them) to get the thing to go the other direction? It has been a while since I mucked with stepper motors. I've checked the IAC and wiring with an ohm meter to verify that the two coils are connected to the ECM "correctly" but that doesn't mean the polarity is right. Might be trial and error time there are no coil polarity markings on the IAC.
Also, I read in one of the papers on the internet that when the engine is turned off, the IAC first resets, then extends all the way, then retracts 145 counts. When I turn off my engine, the IAC doesn't do anything. I do have constant power (orange wires) and switched power (pink wires) to the ECM, so I have that right.
04-08-2003, 07:28 AM
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Car: check
Engine: check
Transmission: check
Re: IAC wiring puzzle
Originally posted by yellow73bb
I have posted about my IAC before, but now I have some more information.
My TB is a Holley 4 barrel unit with integrated IAC.
. . .
The IAC has extended as the count has increased. That doesnt seem quite right
I have posted about my IAC before, but now I have some more information.
My TB is a Holley 4 barrel unit with integrated IAC.
. . .
The IAC has extended as the count has increased. That doesnt seem quite right
Code:
color usage IAC ECM
pin pin
Grn/Blk IAC B Lo C C3
Grn/Wht IAC B Hi B C4
Blu/Wht IAC A Hi D C5
Blu/Blk IAC A Lo A C6
04-08-2003, 07:48 AM
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Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
Re: IAC wiring puzzle
Originally posted by yellow73bb
When I connect the diagnostic pin to ground, the IAC extends,
When the engine is running and warmed up, eventually, the IAC counts will go to zero. When that happens, I can still hear the whistle of the air going through the IAC port, and my car idles at around 1300-1500 RPM. So, I stick my finger over the hole. This brings the idle down to 600-700.
When I connect the diagnostic pin to ground, the IAC extends,
When the engine is running and warmed up, eventually, the IAC counts will go to zero. When that happens, I can still hear the whistle of the air going through the IAC port, and my car idles at around 1300-1500 RPM. So, I stick my finger over the hole. This brings the idle down to 600-700.
With a count of 0 the IAC port should be closed.
Warm engine.
Short A-B together,
key on, engine off.
Wait one full min..
Start engine.
It should be at the min idle setting, ie JUST enough to idle.
If it races, and you plug off the port and the idle drops to a reasonable idle, then the wiring is backwards on the IAC.
04-08-2003, 09:40 AM
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I am pretty sure that is not how my IAC is wired.
I have the wiring harness from a 90 full size van (pared down to essential wiring only for my car), and the IAC connector from a late 80s GM 3.8L engine since the connector for the van was different than the connector on the Holley. The wire colors on the harness and the connector, interestingly, are the same.
However, on the Holley IAC, I get low resistance between the first two pins and the second two pins (A-B and C-D although there are no markings on the connector or the IAC), which I have matched up to the schematic in the manual for my 90 van (the one I drive, not the one I pulled the harness from). When I did this, the wire colors also matched.
On the IAC from the 3.8L engine, the coils were as shown in RBob's diagram (C-B and D-A). The Holley IAC and the 3.8L IAC are wired differently inside. Interestingly, I can get either IAC (the Holley one or the 3.8L one) to move with my ECU, even though they are wired differently internally. I'm not sure if either one of them moves correctly though, more studying is required.
I'll fiddle with it some and see if I can get it to work.
I have the wiring harness from a 90 full size van (pared down to essential wiring only for my car), and the IAC connector from a late 80s GM 3.8L engine since the connector for the van was different than the connector on the Holley. The wire colors on the harness and the connector, interestingly, are the same.
However, on the Holley IAC, I get low resistance between the first two pins and the second two pins (A-B and C-D although there are no markings on the connector or the IAC), which I have matched up to the schematic in the manual for my 90 van (the one I drive, not the one I pulled the harness from). When I did this, the wire colors also matched.
On the IAC from the 3.8L engine, the coils were as shown in RBob's diagram (C-B and D-A). The Holley IAC and the 3.8L IAC are wired differently inside. Interestingly, I can get either IAC (the Holley one or the 3.8L one) to move with my ECU, even though they are wired differently internally. I'm not sure if either one of them moves correctly though, more studying is required.
I'll fiddle with it some and see if I can get it to work.
04-08-2003, 11:47 PM
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They say that memory is the second thing to go, and I can't remember what the first thing was. 
I was remembering my connections incorrectly. Anyway, RBob was absolutely correct. I switched a couple of wires and now my IAC works like a charm. After I let it warm up, I set it for about 2-3 counts and it holds my idle just fine. I rev up the engine, and it counts up and I can verify that more air flows, let it off and the counts drop back down, and less air flows. I never get the whistle now.
Thanks for all the help!
I was remembering my connections incorrectly. Anyway, RBob was absolutely correct. I switched a couple of wires and now my IAC works like a charm. After I let it warm up, I set it for about 2-3 counts and it holds my idle just fine. I rev up the engine, and it counts up and I can verify that more air flows, let it off and the counts drop back down, and less air flows. I never get the whistle now.Thanks for all the help!
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