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How does my car know its rolling?; What activates iac 91 vert
Topic Started: May 31 2013, 12:34 AM (579 Views)
Hogleg
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Midnight Toker

Get a great idle when I unplug the iac, so it's functioning, my car just wants it on all the time for some reason. I was told the iac functions to keep the idle high in between shifts and when the car is rolling and I do remember a similar high idle until stopped when I had my 98.

So. Do you notice while rolling to a stop your idle is high until you come to a complete stop? What sensor senses when the car is rolling? And/Or what sensor controls the iac on a 91 3/5?

I'm trying to avoid deleting my iac. I want the car to function correctly.
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Old Man


My '91 'Vert with AC off idles at 800. Between shifts immediately drops to 1300, and if you hold the clutch in (whether between shifts or coming to a stop) it drops to 800 in about 6 to 8 seconds. Turn the AC on while idleing at a stop and it idles up to 1200 then drops back to 900. Soooo......AC on adds 100rpm........

All this idle is the IAC controlling the vacumn......
that what your looking for?
Edited by Old Man, May 31 2013, 02:13 AM.
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Hogleg
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Midnight Toker

Yes. I want my car to do that! For some reason my iac if always raising the idle to 1300-1500 even when just sitting there. I don't have ac tho. My iac seems to always think I'm rolling. I will have to try holding the clutch in for 10 sec and see if that changes anything. When I unplug the iac the vacuum draw stops and the idle is normal or wherever my stop screw is set.

I assume the PCM controls when the iac should be energized, but what signals the PCM to energize it?

Loving the sig by the way.
Edited by Hogleg, May 31 2013, 02:27 AM.
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RONNIEREDLINE
METRO MAD MAN

i think the computer knows your car is rolling by the vehicle speed sensor, its behind the speedometer itself. VSS.
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snowfish
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Basic GearHead

Have you confirmed that the throttle switch is set properly? :news

http://geometroforum.com/single/?p=716600&t=5009604

You don't have to loosen any screws to verify the readings. Of course if the readings are not correct, then adjustment will be needed. :gamerz

Here's the entire thread to show what the throttle switch internals look like.

http://geometroforum.com/topic/5009604/1/#new

Side note...........when my Wife's 93 speedometer cable broke, the car still went back to idle fine. That tells me that the VSS, located on the speedometer, may not be a huge player in the whole system. :hmm
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Old Man


Hogleg
May 31 2013, 02:21 AM
Yes. I want my car to do that! For some reason my iac if always raising the idle to 1300-1500 even when just sitting there. I don't have ac tho. My iac seems to always think I'm rolling.
'How to' fix the iac:
http://geometroforum.com/topic/4804867/1/
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Hogleg
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Midnight Toker

Thanks for the links snowfish, that will help a lot when I check the tps. Ill report back what I find.

Old man, I found that thread useful when I did that fix on my iac last week. Before the fix I could blow through one end, and after I can't. Good thread.
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