IAC mechanical limitations??

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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Deuce
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cars: TUF355

IAC mechanical limitations??

Post by Deuce »

VR 355, '424, 11p

I notice in the tune the maximum motor position for IAC is set at 196.
Is there a reason for this number for a mechanical reason for IAC movement (bottoming out etc).

High comp, big cam, come ttb mani, and I think I'm going to need more than 196steps to get the target idle rpm without touching the throttle pedal.

I previously had the throttle stop in further (showing 1.35v at TPS) and it was causing a lean out stall after a minute which was obviously a tune 'faulty TPS' type mode.
So I'm now back to 1.04v TPS but need more IAC range.

Any work arounds others could suggest?


I see the 'dylan355vs' file from 11p map is at 255 max steps. So maybe 196 is all the stock Holden 'should' need :?
immortality
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Re: IAC mechanical limitations??

Post by immortality »

Zero steps is fully extended (bottomed out in the TB bore) so max steps is the pintle retracted into the stepper motor.
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delcowizzid
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Re: IAC mechanical limitations??

Post by delcowizzid »

You need to br around 0.5v closed throttle. Doesn't the come manifold have an adjustable bleed on the manifold to add extra air
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Deuce
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Re: IAC mechanical limitations??

Post by Deuce »

immortality wrote: Sun Jun 29, 2025 9:02 pm Zero steps is fully extended (bottomed out in the TB bore) so max steps is the pintle retracted into the stepper motor.
Yeah, but is 196 as far as it goes before mechanically max open? If I digitally add more steps to max limit will it be trying to go further and hurt the IAC internally?
Deuce
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Re: IAC mechanical limitations??

Post by Deuce »

delcowizzid wrote: Sun Jun 29, 2025 10:35 pm You need to br around 0.5v closed throttle. Doesn't the come manifold have an adjustable bleed on the manifold to add extra air
It doesn't have a bleed. But I could add one to the emissions vac hose maybe.
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pman92
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Re: IAC mechanical limitations??

Post by pman92 »

You wont damage anything going more steps, but I wouldn't be surprised if it runs out of travel mechanically.

You need to bypass more air so you require less steps.

Can you adjust the TPS at all? Eg move throttle stop further open, and adjust TPS so it's around 0.5v when closed.
Deuce
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Re: IAC mechanical limitations??

Post by Deuce »

pman92 wrote: Mon Jun 30, 2025 6:54 am You wont damage anything going more steps, but I wouldn't be surprised if it runs out of travel mechanically.

You need to bypass more air so you require less steps.

Can you adjust the TPS at all? Eg move throttle stop further open, and adjust TPS so it's around 0.5v when closed.
I loosened the TPS, but could not get any further rotation on it.
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