Raise Idle Air or Adjust TB screw?
01-23-2007, 08:52 AM
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Staging Lane
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Raise Idle Air or Adjust TB screw? I was just wondering what would be better to do, raise the idle in gear table to around 12 and leave the TB screw stock or lower the idle in gear table to between 8.6 and 9.2 and open the TB screw? Isn't it basically doing the same thing? thanks.
01-23-2007, 10:00 AM
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Two different things...
The idle air table is what airflow the PCM is told the engine needs at idle. You monitor the accuracy of this with the idle trims (STIT's and LTIT's) at various engine coolant temps. If the trims (when added together) are positive, you increase the idle airflow table by that much. If they are negative, you subtract them from the idle airflow table.
The range in which the PCM has to correct for airflow variances is controled by the IAC valve. The amount the IAC valve is open is measured in steps or counts. You can increase the set screw height or drill the throttle body to allow more airflow and reduce the number of steps. To reduce airflow or increase the number of steps, you reduce the set screw height. Basically, the higher the steps/counts, the more open the IAC valve is. Ideally, you want the IAC in the 60~70 step range once the motor is up to operating temps.
The idle air table is what airflow the PCM is told the engine needs at idle. You monitor the accuracy of this with the idle trims (STIT's and LTIT's) at various engine coolant temps. If the trims (when added together) are positive, you increase the idle airflow table by that much. If they are negative, you subtract them from the idle airflow table.
The range in which the PCM has to correct for airflow variances is controled by the IAC valve. The amount the IAC valve is open is measured in steps or counts. You can increase the set screw height or drill the throttle body to allow more airflow and reduce the number of steps. To reduce airflow or increase the number of steps, you reduce the set screw height. Basically, the higher the steps/counts, the more open the IAC valve is. Ideally, you want the IAC in the 60~70 step range once the motor is up to operating temps.
01-23-2007, 10:27 AM
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Staging Lane
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Thanks for the reply, i didn't know how that worked. The reason I asked was because i had a cam put in a couple of years ago at wheel 2 wheel here in Detroit and the tune they gave me had the idle in gear at 12.0 across the board and left the tb alone. But i recently changed my cam-old one 222/226 114, new one-226/230 112. Looking at other peoples files at ls1tuning they have the idle in gear around 8.5-9.2 and i'm guessing they modified the tb hole or opened the screw. Shane at thunder racing actually stopped by my shop one day and looked at my file, he said wheel 2 wheel probably didn't tune it but just used a file close to mine and that the 12.0 raf was to high for my cam. I guess i'll go back and look at my s trims and l trims at idle. thanks.
01-23-2007, 10:30 AM
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Staging Lane
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hey SSpdDmon I just realized you live in Farmington, I used to live there for like 25 years. 10 and orchard then 9 and halsted. Now i live in Brighton.
01-23-2007, 11:21 AM
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Yeah, I'm off of Grand River by M5 for the next 6 months at least. As for your airflow table, it should be somewhere between 6~8 grams/sec. I have a 232/238 cam in my SS and at operating temps, I only need 6 grams/sec.
01-23-2007, 12:08 PM
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I think mine is at 11.5-12grams/sec. at idle. Why is mine so high? I'm idling at 850 maybe 900, i can't remember at the moment it's been awhile since i drove it. What are you idling at?
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01-23-2007, 12:25 PM
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I'm only idling at 875~900rpm...then again, this tune (done by Rapid Motorsports in PA before I owned the car) is still using a stock MAF table, a guess-timated VE table, and fine tuning was done with the IFR, OLFA and PE tables. Plans to do it "the right way" are on hold until the weather clears up.
Last edited by SSpdDmon; 01-23-2007 at 12:30 PM.
01-23-2007, 01:02 PM
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Why do you think my grams/sec. are so high? Too much idle air or tb blade open too much? I was thinking of multipling my maf table by like 103% because of the airlid, do you think that would be a good idea or no. I'm just trying to get it to idle without any dipping and with the l trims slightly negative, i don't want to touch the ifr table-stock injectors. My PE table is 1.2403 across the board and I haven't touch the OLFA table.
01-23-2007, 02:32 PM
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I was just saying that, that was the way the car was tuned (is tuned) when I bought it. I haven't had the opportunity to clean up that tune. With stock injectors, you're right in assuming you don't want to touch the IFR table. The OLFA table is fine in stock form as well. However, your VE table and MAF table need to be dialed in with a WBO2....or at least with the NBO2's during closed-loop operation. You can find instructions on how to do that in the stickies at the top of the forum.
