start up idle tuning?
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start up idle tuning? Ill start with the specs. 98 T/A A4, TSP 228R cam, TSP 102mm MAF, NW 92mm TB, FAST 92mm intake, ported heads, long tubes, stock bottom end LS1.
I think I might have found the answers that I need here but would still like some other ideas just in case that does not work.
The main issue I'm having is the motor surges with the IAC plugged in. You can see in the scan that the IAC is what is causing the surge as it opens and closes. Below is the scan showing the surging IAC and you can see at the end where I command the IAC to 0 and it runs smooth. If I remove and manually close the IAC the car wont idle at all unless the idle screw is adjusted so this is telling me that commanded 0 is not actual 0 on the IAC.
I will try the procedure from the line above tomorrow and report back. In the mean time does anyone else have any ideas?
I think I might have found the answers that I need here but would still like some other ideas just in case that does not work.
The main issue I'm having is the motor surges with the IAC plugged in. You can see in the scan that the IAC is what is causing the surge as it opens and closes. Below is the scan showing the surging IAC and you can see at the end where I command the IAC to 0 and it runs smooth. If I remove and manually close the IAC the car wont idle at all unless the idle screw is adjusted so this is telling me that commanded 0 is not actual 0 on the IAC.
I will try the procedure from the line above tomorrow and report back. In the mean time does anyone else have any ideas?
Last edited by blue-03-ss; Apr 30, 2014 at 03:11 AM.
Thread Starter
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I can back the idle screw out and bring it back to 0% TPS or should I do the relearn? On a few other cars I set the base idle with the idle screw with the IAC manually closed and unpluged. Then let the IAC take over from there is this correct or no?
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From: Monroe,NY
Try a relearn and see if it goes back to 0%. I have never done the raf that way. Look up the Russ K config and use that to fix your raf. You need to do it when car is cold all the way up to hot idle in park then do it again in gear. I would look in the tune repository and find a tune with similar mods and use there raf for a starting point.
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I was using Russ K's config when I did that but I just have not had a chance to have the car idling well enough from cold to run that config. I now have his config set up in the config that I use every day and every time I start the car the RAF numbers on the log change.
Here is a new longer log of what the car is doing. If I command the IAC to 60 steps the car will idle smooth at right at the 1000rpm mark. If I give the PCM full control the IAC will surge as you can see from the log.
Here is a new longer log of what the car is doing. If I command the IAC to 60 steps the car will idle smooth at right at the 1000rpm mark. If I give the PCM full control the IAC will surge as you can see from the log.
Idle stability has not much to do with the running airflow
numbers. Other than that, if they are way off, that's a
"kick" to start the oscillation of the RPM-control loop.
But the tendency to oscillate comes from elsewhere.
Commonly you will end up rich on the in-taken side when
you let wideband readings direct your VE/MAF tuning at
low RPMs, or let the narrowbands trim, on a motor that
has a lot of cam overlap. A little bit of shot-through air
significantly bends the AFR reading. All you can do, to
pull it to "ideal", is declare more air and get more fuel.
But you're also embedding the error into the tune and
chasing a number that is not what the motor really wants.
What the motor really wants, can be found by watching
MAP and trying to get it as low as possible. Open loop.
Bidirectional controls are a good tool here. Real Time
Tuning (HPT) would be the next step, trying out what
you learn about best spark, best fueling, still open loop.
Last you'd alter your closed loop O2 switchpoints to lie
where your actual, found-best-idle-MAP puts their output
so closed loop will pull you to best idle, not some AFR
target.
Improvement can also be found in the P, I, D coefficients
for the idle RPM loop. Good luck finding info here, the
scheme is not really classical PID controller-like. But a
bit of playing around can improve the stability of it. This
is what you'd do last, though - get the motor fed right
and you may not need to go this deep.
numbers. Other than that, if they are way off, that's a
"kick" to start the oscillation of the RPM-control loop.
But the tendency to oscillate comes from elsewhere.
Commonly you will end up rich on the in-taken side when
you let wideband readings direct your VE/MAF tuning at
low RPMs, or let the narrowbands trim, on a motor that
has a lot of cam overlap. A little bit of shot-through air
significantly bends the AFR reading. All you can do, to
pull it to "ideal", is declare more air and get more fuel.
But you're also embedding the error into the tune and
chasing a number that is not what the motor really wants.
What the motor really wants, can be found by watching
MAP and trying to get it as low as possible. Open loop.
Bidirectional controls are a good tool here. Real Time
Tuning (HPT) would be the next step, trying out what
you learn about best spark, best fueling, still open loop.
Last you'd alter your closed loop O2 switchpoints to lie
where your actual, found-best-idle-MAP puts their output
so closed loop will pull you to best idle, not some AFR
target.
Improvement can also be found in the P, I, D coefficients
for the idle RPM loop. Good luck finding info here, the
scheme is not really classical PID controller-like. But a
bit of playing around can improve the stability of it. This
is what you'd do last, though - get the motor fed right
and you may not need to go this deep.
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Thread Starter
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This car is aggravating the **** out of me.. The afrs are in the 14.2-14.8 ish range at idle and the rpms are still bouncing around. The timing and IAC are all over the place. If I hold the IAC and timing steady with the VCM controls in the scanner it will run and idle smooth as can be but if it dont the idle goes from 400rpm-1600rpm. I have had it idling smooth with the PCM in full control for about 5-6 mins then it just dies for no reason.
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Ok, first off on a 1998 PCM you can only log a max of 24 bytes. Your logging 40, and this causes very erratic data. Then back off the TB stop screw to get the closed TPS% to zero.
Russ Kemp
Russ Kemp
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ok thanks I did not know that about the 24 bytes I did notice that it was a little laggy but did not know why it was doing that. I have since closed the TPS via the screw and the TPS is now at 0%. After a little more reading and playing with things and a little help from others I have came up with the file below but still have yet to find a steady idle with out the car stalling.
A big thinks to all that have helped me so far things are getting better but I have still to figure this car out and get it right.
A big thinks to all that have helped me so far things are getting better but I have still to figure this car out and get it right.
TECH Addict
Joined: Aug 2005
Posts: 2,305
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From: Monroe,NY
I looked at a bunch of tunes in the hptuners repository and no one has Raf #'s as high as yours. You have a vacuum leak or you put in way to high #'s in your raf table. I have a picture of yours and a picture of a car with similar mods. Yours is the first picture.
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Newbie to ls1 Help! I have a newly completed 67 c10 with a 5.3 truck engine and i have a GM hot cam in her. She runs pretty good but has an unstable idle and stalls. Manual 5 speed. I sent the pcm back to Street and Performance but still does the same thing. Is there someone in the Austin Texas area that can help tune this thing?
Fred
Fred
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Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
Help! I have a newly completed 67 c10 with a 5.3 truck engine and i have a GM hot cam in her. She runs pretty good but has an unstable idle and stalls. Manual 5 speed. I sent the pcm back to Street and Performance but still does the same thing. Is there someone in the Austin Texas area that can help tune this thing?
Fred
Fred