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Using 8D I want to remove the idle rev up and idle down delay on start up when I start the car it revs up to 2k then slowly drops down. I have removed the "possible rpm adder to commanded idle at start up" which was set to 1000 now it jumps to 1500 and slowly drops down
I cant find the tables for the IAC startup logic, where is the table for idle speed timeout iac steps vs coolant, Im trying to remove or reduce the idle jump and the timer to which the IAC idles down
What XDF are you using? In a 8D MOD xdf I got online I see a "Idle Engine Speed StartUp Delay" , "Spark Advance Decay Rate Startup" and then Startup Vs Temp table for both Enrich (AFR) and SA.
Are you using tunerpro? Can use control+F to bring up the find items window and search parameters with keywords like start, idle, decay, delay, etc.
im using tuner pro but with SAUJP xdf there is a ton more parameters for IAC on SAUJP I believe the issue may be that I have to get the car hot before the changes take place
these are the parameters that I think I need to adjust, I dont see the start up delay logic or "base" parameter to adjust reading the descriptions 3 parameters together control the initial IAC opening
ok still revs to 2k then slowly goes down, none of the parameters made a difference not even the "possible rpm adder to commanded idle at start up" tried increasing and decreasing steps in the tables pictured above
You could potentially reduce the IAC Park Position Counts. That way the car starts up with the IAC not opened so much.
IAC Param, Park Position at Key-off 0x629 Stock is 160.
Maybe try reducing it and see what happens.
Is it the initial shooting up? Or the delay in coming down that's annoying? Or both?
My understanding is the "Park Position" is only what the IAC goes to at key off. Once key is turned on the IAC goes to a predetermined position determined by engine temp.
You could potentially reduce the IAC Park Position Counts. That way the car starts up with the IAC not opened so much.
IAC Param, Park Position at Key-off 0x629 Stock is 160.
Maybe try reducing it and see what happens.
Is it the initial shooting up? Or the delay in coming down that's annoying? Or both?
Both, im diagnosing now i had the wrong iac in there was swapping throttle bodies the iac in there had the smaller pin i have a 88+ IAC housing that has a bigger bore
I believe the park position counts is what will do the trick for the initial jump
With EBL these two are part of the IAC parameter list. There are a couple other modifiers to the powerup initial steps, but this is the base parameter. Park Position is defined as "Steps at which IAC is parked at key-off." While IAC - Powerup Initial Steps is defined as "This tables defines the IAC position during engine cranking. At key-on the IAC moves to this position."
I would imagine 8D having a similar strategy for handling IAC at key off and key on. With IAC Param, Park Position at Key-off 0x629 being your key off and some other setting being what it moves to at key on.
but what im noticing in the log is it starts up at 120 counts then settles to mid 90s before decaying out even though my tables would suggest it should go to 50s there must be more paramaters that add steps
Below comes from your XDF and are listed as descriptions for IAC Param, Idle Engine Speed Startup Delay and IAC Param, IAC S/Up Delay Idle Steps .vs. MAT or Coolant
IAC Param, Idle Engine Speed Startup Delay has a description that states:
Engine Run Time Delay before IAC attempts to control the Idle speed. Prior to that, IAC controlled by the Startup Delay logic.
Although Startup Delay has started (0x0FE b6 IS set since RPM >= Commanded Idle), 0x0114=Startup Delay Counter is NOT incremented until the 0x0119=IAC Warm Park Start Position drops down to <= the Desired Position (0x011D=Warm Park, +20 Steps if 0x003B b7 A/C is On). This means the true Startup Delay period is longer than 600ms by the time it takes from engine start for the IAC to reach the Desired position. At this point, control of the IAC is relinquished by the Startup Delay NOT Done logic.
Factory Default = 600ms
Then you have IAC Param, IAC S/Up Delay Idle Steps .vs. MAT or Coolant which has a description that states:
MAT is used if 0x018 b0=0; Coolant if b0=1
This is the predicted adjustment to the IAC to maintain the target idle RPM. Per RBob, these values used in calculation of warm start-up position:
Base + 'Warm Park Position .vs. Temp' Table + this Table
The base is the learned idle steps. This is developed while the engine is up to temperature and running. It is then stored by the ECM for the next key on (if the battery is disconnected all this goes away and defaults are used).
Added to this learned base value is the steps from the Table at 0x689, WARM PARK POSIT .vs. COOLANT.
Added to this value is the steps from the Table at 0x6A1, IDLE SPEED TIME OUT IAC STEPS .vs. COOLANT or MAT.
Those three values added together make up the warm start IAC position. The time-out steps from 0x6A1 decay out as the engine is running.
Last edited by dabomb6608; 08-15-2024 at 02:47 PM.
Below comes from your XDF and are listed as descriptions for IAC Param, Idle Engine Speed Startup Delay and IAC Param, IAC S/Up Delay Idle Steps .vs. MAT or Coolant
IAC Param, Idle Engine Speed Startup Delay has a description that states:
Engine Run Time Delay before IAC attempts to control the Idle speed. Prior to that, IAC controlled by the Startup Delay logic.
Although Startup Delay has started (0x0FE b6 IS set since RPM >= Commanded Idle), 0x0114=Startup Delay Counter is NOT incremented until the 0x0119=IAC Warm Park Start Position drops down to <= the Desired Position (0x011D=Warm Park, +20 Steps if 0x003B b7 A/C is On). This means the true Startup Delay period is longer than 600ms by the time it takes from engine start for the IAC to reach the Desired position. At this point, control of the IAC is relinquished by the Startup Delay NOT Done logic.
Factory Default = 600ms
Then you have IAC Param, IAC S/Up Delay Idle Steps .vs. MAT or Coolant which has a description that states:
MAT is used if 0x018 b0=0; Coolant if b0=1
This is the predicted adjustment to the IAC to maintain the target idle RPM. Per RBob, these values used in calculation of warm start-up position:
Base + 'Warm Park Position .vs. Temp' Table + this Table
The base is the learned idle steps. This is developed while the engine is up to temperature and running. It is then stored by the ECM for the next key on (if the battery is disconnected all this goes away and defaults are used).
Added to this learned base value is the steps from the Table at 0x689, WARM PARK POSIT .vs. COOLANT.
Added to this value is the steps from the Table at 0x6A1, IDLE SPEED TIME OUT IAC STEPS .vs. COOLANT or MAT.
Those three values added together make up the warm start IAC position. The time-out steps from 0x6A1 decay out as the engine is running.
current settings on those two tables equals 29 steps @ 200 degrees yet i get 80s in the log
"IAC Param, Idle Engine Speed Startup Delay" is at 0 msecs yet there is still a delay
Im going to play with "IAC PID Param, Factor for warm park position determination", "IAC integral gain param,max rpm decline rate in P/N", and "IAC keep Alive learn Param, idle IAC decay rate"
theres much more going on here I do remember using EBL it was much easier to get desired setting for a quite stealth start
It could be that the ECM isn't allowed to decay any faster...
Take a look at
IAC Integral Gain Param, Max RPM Decline Rate if In P/N 0x656
Max RPM Decline Rate if in Park/Neutral. Used in the IAC PID for step determination if Current RPM minus Commanded Idle RPM <= 1587
Factory Default = 150 RPM
This is port injection right? The lower single digit steps are recommended for TBI setups not port setups. Get that higher towards mid 20s. You have the throttle blades opened up too much. Which in turn means it doesn't take near as many IAC steps to raise the idle speed substantially. Your cranking 80 steps will equate to a lower rpm achieved. This will also raise the "base" part of this equation.
IAC Param, IAC S/Up Delay Idle Steps .vs. MAT or Coolant:
MAT is used if 0x018 b0=0; Coolant if b0=1 This is the predicted adjustment to the IAC to maintain the target idle RPM. Per RBob, these values used in calculation of warm start-up position: Base + 'Warm Park Position .vs. Temp' Table + this Table The base is the learned idle steps. This is developed while the engine is up to temperature and running. It is then stored by the ECM for the next key on (if the battery is disconnected all this goes away and defaults are used). Added to this learned base value is the steps from the Table at 0x689, WARM PARK POSIT .vs. COOLANT. Added to this value is the steps from the Table at 0x6A1, IDLE SPEED TIME OUT IAC STEPS .vs. COOLANT or MAT. Those three values added together make up the warm start IAC position. The time-out steps from 0x6A1 decay out as the engine is running.
Last edited by dabomb6608; 08-16-2024 at 07:31 AM.
Using 8D I want to remove the idle rev up and idle down delay on start up when I start the car it revs up to 2k then slowly drops down. Im trying to remove or reduce the idle jump and the timer to which the IAC idles down.
You don't want to remove it... air is denser when cold, the concept is to blend the vehicle's air/fuel during colder temps while gradually lowering the RPM to a more suitable hot engine RPM setting during the warmup process. You can't run the engine when cold at 800-RPM, it will stall when fully warmed up because the air will be less dense at that point, and the system will pull fuel to meter, and you'll surge and stall, so it just can't drop to your desired RPM immediately when cold, only when fully warmed up it can...
Originally Posted by BHR
ok still revs to 2k then slowly goes down, none of the parameters made a difference...
They won't, put them back to their original values...
Originally Posted by BHR
in gear 5-6 in p/n 10-11
This is more than likely your culprit right here. The engine is being commanded to meet certain criteria during the warmup process with no feedback. The throttle blades need to work with the commanded values, but at 10-11 steps at idle with a fully warmed engine, this is telling you the IAC is almost closed, and the throttle blades are opened too much. When you're starting the engine, the RPM "jumps" to 2000-RPM, not because of a value in the scalers, but because you have a rush of incoming air that's not being accounted for. Start the engine when cold again, you live near me and the ambient temp has been about 60*F in the morning lately. Again, put the values in the tune back to where they were. Note the commanded RPM and IAC steps that corresponds with the actual ambient temperature when you start the engine. Once started, don't worry about the 2000-RPM jump, just observe and close the throttle blades slowly while watching the datalogging screen and wait for the RPM to match the commanded RPM, as well as the commanded IAC steps. Once they are lined up with each other for the correct temperature, then shut the engine off, and restart it. The RPM should no longer jump to 2000-RPM anymore...
correct i couldnt achieve desired results, its a very fine line with cold starts and its only in the 60s now and it wouldn't start in the morning with desired settings
IAC Throttle Follower, Time Between Step Movement In P/N 0x659
Time between IAC Steps in P/N. Determines how quickly the throttle follower IAC steps are taken out to allow the idle RPM to drop back to normal when in P/N.
The smaller this value is, the faster the idle should return to normal.
Factory AUJP = 62.5ms
Maybe cut that down to say, 20 ms and see what happens?
That would only be for delay of when IAC steps are removed after throttle application. Wouldn't come into play on start up. His problem is solely his actual idle adjustment on throttle body is too high.
That would only be for delay of when IAC steps are removed after throttle application. Wouldn't come into play on start up. His problem is solely his actual idle adjustment on throttle body is too high.
idle adjustment is now at 25 steps in D dont know what the normal value is read anywhere from 20-60
For the thread i was trying to lessen the cold start up engine speed I have a newer car that tunes with a phone app the option is called cold start delete (disable cat heating) and I like it as I have aftermarket exhaust with no cats on it and on my third gen, I dont always want to have a long loud startup, ULTM8z's and your suggestions have helped
Just looked at a datalog of mine. My IAC at warm idle is around 35. I see a flair to about 1400 rpm on hot or cold starts. Typically it settles within 4 seconds to whatever commanded idle RPM is at that particular engine temp. My hot idle is 800 my 32*F idle is 1000.
Bumping up your warm IAC counts by closing up your throttle idle adjustment will help bring the flair down even more. I wouldn't go over 40 personally.
08-14-2024, 01:57 PM
