High idle & IAC Help
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Joined: Mar 2017
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High idle & IAC Help First, let me say that I am new to tuning and trying my best to learn all I can. I have a 98 ls1 6 speed with 2 bar sd os, no maf. I am using a pcm and harness from a 2500hd. I have copied everything from a stock 98 camaro tune to my pcm as best i could. Im Having a problem with the rpm hanging after I rev it. Its also idling very rich but im sure that is due to my ve being untuned and fuel added during the 2 bar setup. My IAC is 0 at idle, not sure if that is correct. I have added a lot to the Throttle Follower Decay P/N, that seemed to change it some but Im not sure if that is my problem. Could it be the extra fuel causing the rpm hang? Or does something else need adjusting? Can someone please point me in the right direction?
Setup:
'98 LS1 (completely stock)
2 bar maf (PN 12615136)
SD 60# Injectors
Aeromotive BR FPR
Turbonetics T66 Turbo
Setup:
'98 LS1 (completely stock)
2 bar maf (PN 12615136)
SD 60# Injectors
Aeromotive BR FPR
Turbonetics T66 Turbo
Having an IAC of 0 at idle is a huge problem. This will leave no room for the computer to let the idle down. You would typically want an IAC count of around 40-60 at your desired warm idle rpm. Don't be surprised if this goes WELL above 100 on initial cold start. Also, you are correct in thinking you should lean out the idle via the VE table. Your rpm hang is definitely caused in part by the motor already getting enough air to not need the IAC and the rich condition giving the excess air plenty of fuel. I would be very curious as to how a stock ls1 is even able to idle with the IAC closed, which makes me wonder if it is not reporting the correct counts, or if you have a hole drilled in the TB.
Yes, you need to lean it out, but I would not discount any number of other possible issues. The 1998 wiring harness and PCM are bastards that don't play well with other systems. A lesser known fact is that 1999 truck PCMs are also subject to this issue, although that is just something I find annoying, and probably not relevant to this discussion. I am still a bit confused about how your vehicle can even idle with a 0 IAC count.
Thread Starter
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Joined: Mar 2017
Posts: 9
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Ok I will try leaning it out asap. I am waiting on a serial port adapter to arrive (Dont think it'll be here til monday) so i can connect my laptop to Innovate lc-2 wideband because it has to be recalibrated on the signal 2 output in order to log correctly with hpt scanner. My harness and pcm are both from a 2001 2500hd. I have the 98 harness and pcm but decided to go with the truck harness because of the known problems with the camaro harness and pcm. I am confused too about the IAC being 0 at idle, I wasnt sure what the count should be with the turbo installed but it just didnt seem right to me. Im wondering if my intake gaskets may be leaking. What should the engines vacuum be at idle? Maybe i should check it. BTW thanks for helping!!
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