Idle speed
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Joined: Feb 2005
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From: San Diego
Idle speed
This is probably an easy question for a few of you:
What factors go into idle speed in addition to the RPM vs. coolant temp table? I have noticed that the desired idle speed that appears in the log doesn't always match what is in the table for that coolant temp. The target idle speed is almost always higher.
ARAP bin, 6E mask.
Thanks,
Bob B.
What factors go into idle speed in addition to the RPM vs. coolant temp table? I have noticed that the desired idle speed that appears in the log doesn't always match what is in the table for that coolant temp. The target idle speed is almost always higher.
ARAP bin, 6E mask.
Thanks,
Bob B.
Last edited by thebruce; May 29, 2009 at 01:08 PM.
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Joined: Dec 2008
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From: So Pasadena, CA
Car: 1989 Chevy Corvette
Engine: 383 SuperRam 10.7 AFR 195 220/229
Transmission: Fancy Smansy 87 Corvette 700r4
Axle/Gears: 3.33
Re: Idle speed
This is probably an easy question for a few of you:
What factors go into idle speed in addition to the RPM vs. coolant temp table. I have noticed that the desired idle speed that appears in the log doesn't always match what is in the table for that coolant temp. The target idle speed is almost always higher.
ARAP bin, 6E mask.
Thanks,
Bob B.
What factors go into idle speed in addition to the RPM vs. coolant temp table. I have noticed that the desired idle speed that appears in the log doesn't always match what is in the table for that coolant temp. The target idle speed is almost always higher.
ARAP bin, 6E mask.
Thanks,
Bob B.
Thread Starter
Junior Member
Joined: Feb 2005
Posts: 32
Likes: 0
From: San Diego
Re: Idle speed
My wandering idle and high IAC counts problem were solved by getting a new IAC. I'm just trying to figure out why the idle speed the ECU is trying to getis higher than the one in the coolant temp table.
Junior Member
Joined: Jul 2006
Posts: 37
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From: Canada
Car: 82 vet
Engine: 5.7 crossfire
Re: Idle speed
It is air and fuel that governs idle (and spark)
The table is to tell the computer what you want, now you have to help it get there
iac = air
ve = fuel
The table is to tell the computer what you want, now you have to help it get there
iac = air
ve = fuel
Senior Member
Joined: Sep 2007
Posts: 1,091
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From: West Central Ohio
Car: 86 vette
Engine: 383
Transmission: 700R4
Axle/Gears: 3.07
Re: Idle speed
MAF Min Allowable Flow Grs/Sec (LC5FE 6E Arap).
This number should equal the Min air flow set by the Throttle stop.
The Maf reads the amount of air flowing into the engine, then it splits between the IAC position and the Throttle stop amount. The T Blade air that is used should match the grs/sec number (5FE). This is the only way the ECM can then calculate the difference and come up with an IAC count amount.
Example:
If you are opening the T Blade to supply all the air for idle, then the IAC counts will be 0 (zero).
If the T Blades are clear shut then all the air is supplied by the IAC, the counts will be a lot higher.
The OEM setting for the IAC is 20 counts, so the farther away you are from 20 counts, the more "Error" there will be between the desired idle rpm and the actual rpm.
Picture this you have your T Blades set at 1000 rpm and the desired rpm at 500 rpm "Idle RPM vs Coolant Temperature" (LC52E to 53E). If the engine is at normal operating temp and steady load. There is no way for the ECM to remove enough IAC counts to get to 500 rpm.
The commanded RPM will be 500 and the actual will be 1000.
You can read this idle grs/sec directly from the Maf output, by opening the TB to get 0 counts and then closing them and seeing how many IAC counts it takes to keep your true rpm.
After "correcting" the " MAF Min Allowable Flow Grs/Sec". You can then calculate and set your "Gms/sec Scale factor, gms/sec/IAC Count" (LC21F) to be more accurate.
Also set the "Gms/Sec air flow offset for MAF default", so if your Maf fails, the default will be "correct".
Somebody (Tequila boy IIRC) suggested using 1 grm/sec per 100 rpm to get it close. Factory is 4 grs/sec and 450 rpm min TB stop.
Don't forget all the adders "IAC Speed Adder Park/Neutral" (LC52B) 50 rpm, for example.
I hope this makes this rpm "mismatch" easier to understand.
This number should equal the Min air flow set by the Throttle stop.
The Maf reads the amount of air flowing into the engine, then it splits between the IAC position and the Throttle stop amount. The T Blade air that is used should match the grs/sec number (5FE). This is the only way the ECM can then calculate the difference and come up with an IAC count amount.
Example:
If you are opening the T Blade to supply all the air for idle, then the IAC counts will be 0 (zero).
If the T Blades are clear shut then all the air is supplied by the IAC, the counts will be a lot higher.
The OEM setting for the IAC is 20 counts, so the farther away you are from 20 counts, the more "Error" there will be between the desired idle rpm and the actual rpm.
Picture this you have your T Blades set at 1000 rpm and the desired rpm at 500 rpm "Idle RPM vs Coolant Temperature" (LC52E to 53E). If the engine is at normal operating temp and steady load. There is no way for the ECM to remove enough IAC counts to get to 500 rpm.
The commanded RPM will be 500 and the actual will be 1000.
You can read this idle grs/sec directly from the Maf output, by opening the TB to get 0 counts and then closing them and seeing how many IAC counts it takes to keep your true rpm.
After "correcting" the " MAF Min Allowable Flow Grs/Sec". You can then calculate and set your "Gms/sec Scale factor, gms/sec/IAC Count" (LC21F) to be more accurate.
Also set the "Gms/Sec air flow offset for MAF default", so if your Maf fails, the default will be "correct".
Somebody (Tequila boy IIRC) suggested using 1 grm/sec per 100 rpm to get it close. Factory is 4 grs/sec and 450 rpm min TB stop.
Don't forget all the adders "IAC Speed Adder Park/Neutral" (LC52B) 50 rpm, for example.
I hope this makes this rpm "mismatch" easier to understand.
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