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IAC Valve too pussy for the job???

Apoc

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Hey all,

In my newest battle with my cars idle (too fast... which i thought id sorted) i fitted up a new TB which i cleaned up nicely which also had a new TPS with it.

After cleaning up my IAC and whacking it in the TB i adjusted the butterfly so that i couldnt see any light around the edges (figured thatd help prevent fast idle and i could just crank it open till car idled at a decent pace).

After I fitted all of it to the car i kicked the car over and i could here this massive sucking noise and the car was still revving too high, had a look no air leaking aroud the butterfly or at least the butterfly hadnt been sucked open. So i stuck my finger over the port for the IAC valve and the car stalled (thank god no other massive vacuum leaks :thumbsup: ) also the sucking was all happening from the IAC port.

So if all the air is being sucked in through the IAC port and the car is still idling too fast does this mean my IAC valve is too pussy to close up properly??? (it does work to some degree, just as the car seems to be approaching a decent low idle speed it runs out off action, i can use my finger to do the job sliding it over the IAC port closing it off bit by bit and i can get a nice low idle).

So just to make it short and sweet now....

Finger over IAC port car stalls
finger partially over IAC port idle control
IAC valve doin its business car idles high

Time for new IAC valve???

Cheers, Apoc.
 

fitzy2005

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u may have the iac valve pintle back to far, its ment to be 28mm from bottom to tip, it may be locked in a certain position..
 

Boonz

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did your engine have a bellmouth??? if it was removed it can cause a high idle sometimes, how long was the computer left to reset?? does the butterly have any freeplay, did you reset the IAC tot he right length.........

theres a thread about setting the IAC to the right length before re-installing
 

Doctor Bob

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the iac will reset if you hold the revs over 2000 for 20 seconds.
setting it to any measurement or setting is a waste of time, it will move as soon as its running anyway.
sounds like it needs to reset

Cheers rob
 

immortality

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to set the butterfly, slowly cover the IAC port with your finger. when the port is fully covered, open or close the butterfly untill then engine is idling just above the point where the idle is rough(500-600rpm), but it should be less then the 750 - 800rpm as this is where the IAC will try to set the idle. once the base idle is correct, reset the ecu by disconnecting the battery for 30 sec, then reconnect and rev the engine to 3000rpm for 15 seconds and let it return to idle, it will intially drop the idle to about 1500rpm and then slowly drop till it reaches it's final position which should be to 750-800rpm. whne you do these adjustment have the engine up to running temp and have all the accesories turned off. if the idle still doesn't reset properly you could consider getting another AIC valve. good luck
 

Apoc

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Cheers all for the feedback,

fitzy2005 - "u may have the iac valve pintle back to far, its ment to be 28mm from bottom to tip, it may be locked in a certain position..."

Nope its not locked up dude it is doing something just not enough maybe...

boona'[email protected]_pace - "did your engine have a bellmouth??? if it was removed it can cause a high idle sometimes, how long was the computer left to reset?? does the butterly have any freeplay, did you reset the IAC tot he right length........."

Nope its a series I, no bellmouth, the computer was left to clear long enough as i have needed to reset recently due to some detonation setting off the sensor. The new (2nd hand) TB is fine it seems, no freeplay, the spring is tough enough, the butterfly doesnt bind, opens 100% and closes virtually 100%.

I also believe that the resetting of the IAC pintle to any length is unneccesary.... However i may be wrong im not a 100% sure how it works the only way i see that setting the IAC pintle to any length making any difference is that it is driven by a stepper motor. This stepper motor is then given a signals, steps to drive either direction which is monitored by the ECU.
This would give a set range (number of steps) say 3mm, either side of where the pintle calls home, say 28mm (giving a pintle range of 25 - 31mm in theory only!!!). If my pintle was then set to say 27mm for example i could under these conditions see that it wouldnt work properly as my range would then be 24-30mm...

Does anyone know mechanically whats in the IAC pintle ???

Doctor Bob - "setting it to any measurement or setting is a waste of time, it will move as soon as its running anyway." I agree for now... :)
"sounds like it needs to reset" Nope have done that already.

immortality - "blah blah blah" lol :), cheers man that all seems to make sense to me. I will have a crack at that and failing that working i will try to get another IAC valve, Not a new one however as SuperCheap wanted like $160 for one and the dude said there was ones for like $300!!!! as you could imagine my jaw hit the floor i picked it up long enough to exclaim, dude its like this big unless its made of gold i think ill go to the wreckers ;)

Once again cheers all, if my answers seem abrupt im sorry, i take all responses into account as im no expert (and one of you might be...).

Apoc out.
 

Apoc

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Dug up some new information that may change my mind on the

To adjust or not to adjust IAC Pintle position debate....

According to a website i found

"General Motors EFI engines typically have 4-wire, 56 Ohm stepper motors. (The measured DC resistance can be ~35-45 Ohms). Two GM style motors are available. On type screws into the throttle body as a unit. The screw-in type IAC has a M20 x 1.5 thread with a square, 4 pin connector." "The O-ring style, bolt-on style GM IAC motor uses an 'in-line' 4 pin connector. It is attached to the throttle body with two small machine screws"

SO IT IS DRIVEN BY A STEPPER MOTOR!!!! :my:

So my theory about the IAC pintle described above may be right!!! I think ill whip mine out and get the steel ruler onto it.

Heres a picture also that came with the text... Im thinking ours looks pretty similar to the one on the edit: right (dont know left from right lol)
Apoc out.
 

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Doctor Bob

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Yesa its driven by a stepper motor. adjusting it to any measurement before fitting is a waste of time.
it will move to where it needs to be to control the idle speed to where it has been set in the calibration
resetting it sets the zero point, thats why you do it...
do what immortality says & it should be ok

trust me ok.

Rob
 

Apoc

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Doctor Bob - "resetting it sets the zero point, thats why you do it..."

So the pintle moves from where it is to fully in or fully out when you reset it? or somewhere else within the range?

I would like to have my pintle out when i reset it to see what it does for the following reason.

If the pintle does not move to fully in or fully out, or to a home in between the range (which id like to know how it senses this position). And if the reset simply resets the ECU to think the pintle is at a home at its present location then i can see a problem as what if your pintle was fully extended after cleaning and you whack it in and reset. The pintle goes nowhere (its position is still fully extended after reset) and the ECU thinks this is home it then it trys to move down to start the car say... then the ECU goes; crank down a few notches, hmmm not much happening here go down some more, whooaaa cant go down more u should be fully down now dont want to make you constantly drive down while i try to get a better idle could bugger you up...

I dont want to start an arguement just really would like to know EXACTLY how the IAC valve resets, and functions. Untill i find someone who says; the IAC valve has no ranges therefore blah blah, or it homes to in, out, or to another point blah blah, i will continue to probe for more info please tell me more if you know it. You seem quite convinced that it doesnt need move you must have some reason for being so adament...

Cheers Apoc.
 

Doctor Bob

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if you run the car with the IAC motor out it will rev high due to the vac leak
the ECM will attempt to drive the pintle out to slow it down, the IAC will fall apart.
when the engine is revved over 2000 rpm for 10 seconds it does a reset.
the pintle will step out for a set time, this time is calculated to allow for all 255 steps of its travel to ensure it has closed completely, then it will step in to its required base number of steps. this base setting is adjusted constantly by the ECM to maintain the correct idle speed. This setting is adjusted by other inputs such as ac input switch, temperature & system voltage.
The later systems do an iac reset at each ignition off to maintain a better control of the idle.
hope this helps you understand it better, this is why setting it to any particular position is a complete waste & in untrained hands can damage the delcate gearing in the motor.

Cheers Rob
 
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