Tune question
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Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Tune question
Is it OK to tune with my car's IAC at 1, with a warm engine? My fuel trims are good. No vacuum or exhaust leaks. Idle screw never been messed with. Anyways, do I need to bring up the IAC counts before tuning?
Thread Starter
Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Melting Slicks
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From: KB7TIF Ville NV
Thread Starter
Race Director
Joined: Oct 2011
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
I will. To my knowledge, there aren't many vacuum lines in the LT1's. Cause I've looked and looked
.
I only count 11 vacuum lines. The smoke test revealed no leaks. I've never tried with starting fluid, but I will. And sorry guys, I know I have been chasing this forever.
With that said, my desired idle speed is 550 rpm. My idle is 550 to 575 rpm.
. I only count 11 vacuum lines. The smoke test revealed no leaks. I've never tried with starting fluid, but I will. And sorry guys, I know I have been chasing this forever.
With that said, my desired idle speed is 550 rpm. My idle is 550 to 575 rpm.
Last edited by 1993C4LT1; Jul 13, 2016 at 08:45 PM.
Melting Slicks
Joined: Dec 2008
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From: Mystic CT
550??? big fan of 750 to 800 water pump works better alternator works better power steering brakes etc. Had a client that wanted 780 hp. SBC to idle at 900 so as to not drag them into a corner sports car racing yet no traces on the data showed less than 5000 and had monster rotors and 6 pot Brembos that would stall the engine at any speed.
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Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
I'm not putting a different cam or anything like that, just longtubes, no cats and 1.6 roller rockers. The FSM calls for the same idle, in gear, with a warm engine.
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Melting Slicks
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What are you idling in gear with a warm engine now? If you are idling higher than what the FSM says, that might be more evidence of a vacuum leak OR it might be indicate a stuck open IAC.
Safety Car
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From: Glenbeulah Wi
Bottom line is yes, if you run out of IAC adjustment and mechanically all is well then you can adjust the throttle valve.
Le Mans Master
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From: near the thumb in the mitten
What is TPS reading and Min Air Rate? If you block off throttle body will engine stall? What is INT/BLM at idle? If you have vacuum leak it should show there? It's possible there in nothing wrong. You have a strong running engine where the internal friction has reduced over the years allowing engine to idle faster. I would wait until your done with your bolt ons before tuning.
Last edited by Kevova; Jul 14, 2016 at 09:55 AM.
Thread Starter
Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
What is TPS reading and Min Air Rate? If you block off throttle body will engine stall? What is INT/BLM at idle? If you have vacuum leak it should show there? It's possible there in nothing wrong. You have a strong running engine where the internal friction has reduced over the years allowing engine to idle faster. I would wait until your done with your bolt ons before tuning.
I didn't see minimum air rate, let me see if I can find it.
To block off the throttle body, I need to take off the air intake right? And just block it off with my hand?
Left BLM at idle: 129-132
Right BLM at idle: 115-120
I'll have to get the INT's.
Le Mans Master
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From: near the thumb in the mitten
Yes disconnect air intake at throttle body and block T/B off with a rag or something similar. BLM doesn't indicate lean but a little rich on right side. I would look at check valve on right side of intake since they deteriorate with age. TPS is a little towards the high side so I might adjust idle screw watching IAC counts and TPS values. TPS shouldn't read lower than .50 ECM is still going try keep you a same idle speed as you have now.
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2025 C4 of the Year Finalist - Modified
The Left BLM will go lean at part throttle, in some cases. Highest I saw in my datalog from yesterday was 145, it doesn't stay there forever tho. Just a short time. And thank you for telling me how to block off the TB. If it stalls when I block it off, what does that mean?
Safety Car
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From: Poughkeepsie New York
The Left BLM will go lean at part throttle, in some cases. Highest I saw in my datalog from yesterday was 145, it doesn't stay there forever tho. Just a short time. And thank you for telling me how to block off the TB. If it stalls when I block it off, what does that mean?
Le Mans Master
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From: near the thumb in the mitten
INT BLM typically with go up on acceleration ECM is adding fuel. They should stabilize and come back down when you move in to a cruise mode. On decell they can go low since ECM is cutting fuel back and engine vacuum is high.
Lt1 uses multiple O2 sensors
Lt1 uses multiple O2 sensors
Last edited by Kevova; Jul 14, 2016 at 12:21 PM.
Thread Starter
Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
At cruise speeds, yes, BLM's are pretty near perfect. Since mine is a 93, it only has two o2 sensors.
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
I let it get up to 180 Fahrenheit. I put two microfiber towels and my hand over the TB. It did cause it to turn off. I left the IAT sensor connected, if that matters.
And I did replace the check valve a while back, on the passenger side. It was bad.
And I did replace the check valve a while back, on the passenger side. It was bad.
Last edited by 1993C4LT1; Jul 14, 2016 at 10:05 PM.