IAC count question
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
IAC count question
Trying to solve a slight idle problem in my 1985 stock L98 (varies between 580-620).
I scanned the car and the IAC counts are all over the place, then slowly decrease as the temp goes up.
I think I have a vacuum leak (I have yet to verify that), and I read that the IAC can reveal that.
Can anyone tell me what values I should be getting here?
starts at about 140, and goes down into single digits.
I scanned the car and the IAC counts are all over the place, then slowly decrease as the temp goes up.
I think I have a vacuum leak (I have yet to verify that), and I read that the IAC can reveal that.
Can anyone tell me what values I should be getting here?
starts at about 140, and goes down into single digits.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
The counts go down as the engine warms up because as the engine warms, the ECM calls for a lower idle speed. Even the high side on that idle speed range is none too high. I'd start by making sure the IAC and passages are clean. I would expect the idle speed to be ABOVE spec, with a vacuum leak, not lower. It is possible you have a little of both.
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Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Originally Posted by mikey whipreck
Trying to solve a slight idle problem in my 1985 stock L98 (varies between 580-620).
I scanned the car and the IAC counts are all over the place, then slowly decrease as the temp goes up.
I think I have a vacuum leak (I have yet to verify that), and I read that the IAC can reveal that.
Can anyone tell me what values I should be getting here?
starts at about 140, and goes down into single digits.
I scanned the car and the IAC counts are all over the place, then slowly decrease as the temp goes up.
I think I have a vacuum leak (I have yet to verify that), and I read that the IAC can reveal that.
Can anyone tell me what values I should be getting here?
starts at about 140, and goes down into single digits.
I think to answer your question counts moving that much to control or adjust idle that much sounds like a vac leak. On a stock set-up I thought the counts should be around 20. hope this helps
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
I should have mentioned first, that the IAC is new, and the passage and throttle body are clean. New gaskets for the throttle body and passages too.
I didn't know that IAC counts when down as the engine warms, It seems as though my IAC is working in that reguard, except that the lower values are way lower then the should be from what Mseven says...
My counts dropped to 8...
The idle isn't off by too much, so I doubt the answer will be obvious.
I'm going to keep searching for that vac leak if you guys think that could be present, but what else effects the IAC counts? A/F ratio? Fuel pressure?
Originally Posted by CFI-EFI
The counts go down as the engine warms up because as the engine warms, the ECM calls for a lower idle speed. Even the high side on that idle speed range is none too high. I'd start by making sure the IAC and passages are clean. I would expect the idle speed to be ABOVE spec, with a vacuum leak, not lower. It is possible you have a little of both.
RACE ON!!!
RACE ON!!!
Originally Posted by mseven
I think to answer your question counts moving that much to control or adjust idle that much sounds like a vac leak. On a stock set-up I thought the counts should be around 20. hope this helps
The idle isn't off by too much, so I doubt the answer will be obvious.
I'm going to keep searching for that vac leak if you guys think that could be present, but what else effects the IAC counts? A/F ratio? Fuel pressure?
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
counts dropped to 8... The idle isn't off by too much, so I doubt the answer will be obvious. I'm going to keep searching for that vac leak if you guys think that could be present, but what else effects the IAC counts? A/F ratio? Fuel pressure?
The number is actually a point where the computer can compensate. As I stated I think is 20 counts, 10 may not be far off. If you get the IAC counts to low it will try to drop below the programmed idle , and if to high (out of range) will not let the idle come down to the programmed idle speed.
Mine being modified (and idle programmed for 825) 40 counts is what I am looking for, but anything from 30 something to 47 or so is allowing the IAC to be within range to compensate.
One thing I like to do is after cleaning the IAC with throttle body cleaner is to put a drop of oil on the stepper motor shaft. Maybe going back through it and re-set the min. air wouldn't be bad idea either.
Last edited by mseven; Jun 27, 2006 at 09:35 PM.
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by AGENT 86
Did you remember to put the little vac line on bottom of TB (drivers side)
I don't have access to my car until this weekend, though. So I can't do anything till then.
Drifting
Joined: Apr 2003
Posts: 1,379
Likes: 4
From: rome ny
the iac counts need to be 20-50 to control idle properly. there are 2 ways to adjust your iac counts, open or close the thottle blades until desired counts are met. if you try to open the blades to lower your counts and it is open all the way drill 1 1/16" hole in each blade then readjust your blade position.
blades opened more = lower iac counts ...
blades opened more = lower iac counts ...
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by mseven
Fuel pressure will definely effect IAC counts.
I also believe that an otherwise healthy L98 won't idle as high as 580-620 rpm on only the air, 8 IAC counts can provide. If the minimum air adjustment is proper, there must be a vacuum leak.
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by mos90
the question is. what is the target idle speed for this particular car?
The comments made thus far seem to point towards a vacuum leak, which I suspected and thought that the IAC might confirm.
Thanks for the input, and I'll be messing with the car this weekend. I'll let you know if I find anything.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi. I have an 85 4+3 and I think that an idling of 580-620 seems within acceptable limits. False air may be the reason and one place there may be false air making this small variation may be in the throttlebody shaft. The wear and tear there may cause some air to come in. And that will change as there will be too much room for the throttle shaft to move in. I have a much more progressive cam than stock which made the idle vary more than this. I have accepted that as the idle is a bit lopy. But a variation of 40 rpm is not much after my opinion, but nothing is better than if you really find the reason and made it stock stable.
