Idle Operation Part 1
11-27-2004, 12:02 PM
#21
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Originally Posted by Bink
My guess is look at your "Throttle Cracker" table - too much airflow above 5mph. If your Idle AirFlow (RAF) is too high it will hand until the car stops. Hope this helps some.
I was also wondering if it could be linked to my MAF Calibration table throwing everything off. It too is still at stock values even tho I have billet MAF ends & a ported TB. Tho I didn't have this problem until I added the cam.
Last edited by WAHUSKER; 11-27-2004 at 12:14 PM.
11-27-2004, 12:21 PM
#23
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No, but I was wondering if that was the thing to do in those cells. Like I said it's all stock right now. (as are all the throttle follower tables)
My Throttle Cracker Table
400rpm 1000 1600
0mph 0 0 0.2
4mph 1 0 0.6
8mph 0 0 0.65
12mph 0 0 0.7
16mph 0.4 0.5 0.7
20mph 0.4 0.5 0.8
24mph 0.5 0.55 0.8
28mph 0.5 0.6 0.9
32mph 0.6 0.65 0.9
36mph 0.65 0.65 2
My Throttle Cracker Table
400rpm 1000 1600
0mph 0 0 0.2
4mph 1 0 0.6
8mph 0 0 0.65
12mph 0 0 0.7
16mph 0.4 0.5 0.7
20mph 0.4 0.5 0.8
24mph 0.5 0.55 0.8
28mph 0.5 0.6 0.9
32mph 0.6 0.65 0.9
36mph 0.65 0.65 2
11-27-2004, 01:11 PM
#24
No, I wouldn't zero them out. Does it cruise indefdinitely with the throttle closed - i.e. no decay whatsoever?? If so, then I would try reducing the Throttle Cracker Airflow by 15% 2000RPM, 36 mph and down. Leave the 1.000 island, at 400 RPM and 4 mph, alone - don't change it. Take it out and see how it does - scan it.
11-27-2004, 03:57 PM
#26
Originally Posted by WAHUSKER
The 1 @ 400rpm is so it doesn't stall, correct?
11-27-2004, 11:01 PM
#27
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Originally Posted by Another_User
So basically, there is a conversion for g/sec to IAC counts, yes? Because it makes no sense to me that Running Airflow would be the same no matter what you drill your throttle body to, or how you change your set screw. Because making those changes instead of changing Running Airflow works. So is there some conversion, so you can log your actual IAC counts and correct your Running Airflow table? Or is there some variable we cannot change yet, like Airflow vs. Actual IAC Position?
11-28-2004, 12:06 AM
#28
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from my post
After the "Desired Idle Airflow" is calculted , it is then translated into an "Effective area" value in square millimeters (mm2). This is the cross sectional area required to deliver the airflow desired (taking into account air density and pressure ratio across the throttle/IAC). Now at this point the calculation branches to either IAC or ETC.
If IAC is installed the "Effective Area" is translated into a number of "steps" that delivers this area (a table of IAC Steps vs. Effective Area).
If ETC is installed then there is a single value that translates "Effective Area" into "Desired throttle area percent" units of % area per mm2. This number is then handed over to the ETC routines that control the ETC TPS %.
After the "Desired Idle Airflow" is calculted , it is then translated into an "Effective area" value in square millimeters (mm2). This is the cross sectional area required to deliver the airflow desired (taking into account air density and pressure ratio across the throttle/IAC). Now at this point the calculation branches to either IAC or ETC.
If IAC is installed the "Effective Area" is translated into a number of "steps" that delivers this area (a table of IAC Steps vs. Effective Area).
If ETC is installed then there is a single value that translates "Effective Area" into "Desired throttle area percent" units of % area per mm2. This number is then handed over to the ETC routines that control the ETC TPS %.
11-28-2004, 07:10 AM
#29
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But that doesn't take the idle hole or set screw into account? I don't see where it "subtracts" this, because it would have to in order to effectively use the running airflow table. So is there a value that is set for "base airflow (non-iac/etc controlled)"? If there isn't, then running airflow can't be measured in airflow, it would have to be in steps.
Like here, his airflow requirements at idle didn't change, but you recommend that he set back his running airflow to account for more flow of the throttle body...
My point is, based on what you say, if the running airflow is right, then there is nothing to trim, regardless of what changes you made to the throttle body. Unless there is a "base airflow non-iac/etc controlled", or the "running airflow" is actually measured in counts.
Originally Posted by gameover
Yeah the adaptive idle (RPM learn) would learn you back, but you could be hitting the adaptive limits. In anycase setting your base Running Airflow lower would fix it...
My point is, based on what you say, if the running airflow is right, then there is nothing to trim, regardless of what changes you made to the throttle body. Unless there is a "base airflow non-iac/etc controlled", or the "running airflow" is actually measured in counts.
Last edited by Another_User; 11-28-2004 at 07:25 AM.
11-28-2004, 07:27 AM
#30
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it doesn't care, this the calibration of the IAC. ie. how much airflow thru the IAC do i need to move the engine RPM up or down.
The hole in the TB (or set screw) just adjusts the IAC dynamic range to be "useful". eg. if you want to idle your engine at 1100 RPM it's probably not a good idea to burn ~200 steps of your IAC to get your idle RPM, leaving you only 110 for "adjustment". Far better to drill the blade or adjust the set screw to give you IAC counts in a much lower range at idle.
Chris...
The hole in the TB (or set screw) just adjusts the IAC dynamic range to be "useful". eg. if you want to idle your engine at 1100 RPM it's probably not a good idea to burn ~200 steps of your IAC to get your idle RPM, leaving you only 110 for "adjustment". Far better to drill the blade or adjust the set screw to give you IAC counts in a much lower range at idle.
Chris...
11-28-2004, 09:33 AM
#31
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Originally Posted by gameover
it doesn't care, this the calibration of the IAC. ie. how much airflow thru the IAC do i need to move the engine RPM up or down.
The hole in the TB (or set screw) just adjusts the IAC dynamic range to be "useful". eg. if you want to idle your engine at 1100 RPM it's probably not a good idea to burn ~200 steps of your IAC to get your idle RPM, leaving you only 110 for "adjustment". Far better to drill the blade or adjust the set screw to give you IAC counts in a much lower range at idle.
Chris...
The hole in the TB (or set screw) just adjusts the IAC dynamic range to be "useful". eg. if you want to idle your engine at 1100 RPM it's probably not a good idea to burn ~200 steps of your IAC to get your idle RPM, leaving you only 110 for "adjustment". Far better to drill the blade or adjust the set screw to give you IAC counts in a much lower range at idle.
Chris...
11-28-2004, 04:57 PM
#32
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Originally Posted by Another_User
Aha. So the value is only the amount of air that should be flowing through the IAC. That's what I wasn't sure about...I haven't had much luck treating it as just IAC running airflow. For instance; when my car is cold I see idle airflow of about 13 g/sec and my desired idle airflow is about 14.5 g/sec with 145 IAC steps, with a stable idle. Is this an issue with 98 vehicles like mine?
11-28-2004, 05:59 PM
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Originally Posted by gameover
hard to tell, could be your IAC is clogged up a bit and has to open more to get the same airflow? it's (or the MAFs) calibration could be out? I never pay much attention to the MAF airflow relation to the IAC desired.
08-15-2005, 04:57 PM
#34
Originally Posted by gameover
What else?
In addition to the Idle Airflow routines the PCM also has an RPM based idle spark correction "closed loop" operation that it uses to control the idle RPM. Since the spark advance can move much faster than the IAC, it can provide very fine control of idle speed. When logging you will see this as a jagged spark advance chart, most noticable with cams at lower idle RPMs where the spark advance generally oscillates between it's min/max allowed values as the engine "cams" at idle.
END.
08-15-2005, 07:06 PM
#37
you can hold the timing at idle steady but deleting the overspeed and underspeed tables. this however will not allow, in most cases, a smooth idle. i adjsuted my spark changes from 25 rpm delta and up in half deg increments starting at 1, i also adjusted the underspeed settings to if the idle dips really low the timing will help it recover on those freak rpm dips on let off. i plan to try and write up a new file of everything i have done so far
