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Thread: iac steps
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04-28-2017, 10:04 AM #1
iac steps
I know it's gotta be covered somewhere but can't seem to find it. I have swapped over to a 52 mm tb and my iac counts are sitting are 112 to 120 at idle. My question is where do I exactly drill the hole to help with idle air.
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04-28-2017, 10:19 AM #2"The Rock"
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04-28-2017, 10:27 AM #3
So how do I adjust it for idle counts
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04-28-2017, 11:15 AM #4Xtreme Member
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Supporting Memberyou don't drill unless absolutely necessary. first thing though is run the throttle body blade stop screw out 1 turn. then check iac counts at hot idle in closed loop. continue cracking the blades open until your iac counts are between 30-50 hot idle in closed loop
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1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
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04-28-2017, 02:34 PM #5
if you follow the advice of Popo and adjust the stop screw on TB.....you will then need to slot the holes in the TPS outer housing so you can "rotate" it back so your TPS vdc is restored correctly. (.67vdc +/- blades closed and 4.5 vdc full open)
You will also need the PCM re-calibrated or tranny failure will follow if a A4 car
IAC counts want to be 30-35 (32) at idle with engine at operating temp
IMHO a stock TB bored to 52, assuming your build even needs a larger TB, is a better TB. Often H/C builds do require the stock hole to be drilled out 1/64-3/64" larger but never blindly drill, use scan tool to read IAC counts. 1/64" makes quite a difference (lowering) IAC counts96 BBB 383/T56
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04-28-2017, 02:36 PM #6Xtreme Member
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Supporting Membernever had a tranny fail without tuning when adjusting for iac and tps, what is the issue you speak of?
everything else is correct, but we both left out that most aftermarket throttle bodies don't have the proper iac circuit in the first place and that leads to split blms and other idle issues.
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1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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04-28-2017, 03:03 PM #7
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04-28-2017, 03:05 PM #8Xtreme Member
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Supporting Member2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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04-28-2017, 03:32 PM #9
because line pressure to tranny (auto) is based on TPS position. larger TB the PCM needs re-tune to correct for the lower line pressure as the larger TB blade position is different per vdc than the smaller stock TB. The lower line pressure will cause slippage in tranny and thus fail.
also if you do the "crack the TB blades open" to try and get larger aftermarket TB's to idle right because IAC counts are to high.....you need to then correct the TPS to correct vdc voltage by slotting the holes or you will have line pressure issues....which can result in tranny failure (auto). The PCM reads the vdc from the TPS to adjust line pressure to the tranny as it increases from .67 with blades closed to 4.5 vdc blaides full open96 BBB 383/T56
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04-28-2017, 03:35 PM #10Xtreme Member
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Supporting Memberah, I see, I know you have to slot/adjust tps for voltage, figured that was a given, but if you're swinging that far Imho you have more than just the issue of a bigger throttle body.
but the pcm has a voltage range for closed tps voltage, ie .45-.72 for idle. I always set mine to .57 since most stock cars that's about where it's at, give or take a few mv. just in my experience never heard of the tps issue affecting the transmission as long as it's within .45-.72 at "closed" and does not exceed 4.5v wot.
Sent from my SAMSUNG-SM-G935A using Tapatalk2021 Charger Scat 392
1994 Firebird Formula 381 stroker - Carrying the torch! - 9.90 @ 134.3mph on a 200 shot
The wrench/driver for LTConvert's 94 Z28- Ellwein 383/LE Trickflows/ D1SC / CPT Ultra Pro Race 4L60E
10.78 @ 125mph. Shooting for 9.99 for Frank Cahall!
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