when I set my desired idle to say 700rpms and crank the engine it idles at that rpm for a min or so and then it slowly climbs up another 100rpms. I can see the desired idle in the scanner showing 700 but then it starts counting its self up automatically, its driving me crazycan any one help?
you need to log IAC counts and ignition timing. if IAC counts are at zero when rpm climbs then you have a vacuum leak somewhere and the IAC is completely shut and can't control idle any more.
you really need to post your tune and a log of it happening so the tuners on here can help you better instead of guessing at what is causing your problem
okay I attached a log and a tune file I have it set at 600 in the tune file to make it idle at 700
your timing and your overspeed and underspeed spark tables are set up wrong. notice in your log how your timing is jumping between 36 and 20? also your timing table is extremely aggressive for these style engines on pump gas - these LS engines like less timing than traditional small block chevys. I modified your over and underspeed tables and also check out what I did to your low octane table - you may want to copy it over to your high octane table (it is still a pretty aggressive table for these engines). Also note that I decreased your idle timing areas to 20 degrees and made all tables match - use your compare and check the differences. it is easier for me to just make these changes and attach your tune for you to compare to your old tune then to try and explain everything
Oh crap I forgot to say what engine I have it is a sbc gen 1 with a cam running a 24x conversion. It's not a lt1 tho im using the LS throttle body on a edelbrock efi intake.. Im trying to learn to tune with the books from the tuning school and they say to adjust the overspeed/underspeed in that way to follow the cam profile. I may have went too far with the -8&8 degrees tho. I'm new to this so excuse my ignorance.
Also I did not tune this engine. I had someone else off this forum tune it over the web, and they wasn't much help so I'm trying to fix the issues I have, my self now.
ahhhh... this is a traditional sbc.
take a look at how I set up the overspeed and underspeed tables - these settings will work better regardless of what engine type. -8 and 8 degrees are what I set them up to as well but they need to gradually get to that number as rpm deviates. the way the timing is jumping from 20 degrees to 36 in your log like its on a toggle switch is keeping the pcm confused and struggling to make the proper corrections to maintain commanded idle speed. hope I am explaining this good enough - I am not so good with a keyboard sometimes.
ohhh now I see why the stock tables looked something like that. so the rpm on top of the table is- if its over or under target idle it adds or takes away that amount of timing? maybe I didn't understand what the book was talking about. Any clue to why the rpm counts its self up like it does tho. I mean I can just leave it set like it is to get my desired idle if that's the way it has to be.
- yupso the rpm on top of the table is- if its over or under target idle it adds or takes away that amount of timing?
- the pcm uses timing first (or its quick reflex) to control idle speed and then idle air trims second (or slower reflex). with your timing jumping around so much and not really controlling idle to begin with I don't think the pcm is able (or willing - lol) to use idle air trims to control idle either.Any clue to why the rpm counts its self up like it does tho.
once your timing is stable (fluttering up and down a few degrees is normal - so stable is a relative term - toggling 20 to 36 is not stable tho) - then you can log your desired idle airflow and compare to your base running airflow. it is important for your base running airflow to be close so the computer isn't having to adjust much(idle air trims). after viewing your log I think as soon as you fix your timing your idle problems will go away - your iac counts look fine to me and I doubt you will need to change your raf table - I am just attempting to explain to show how spark and airflow tie together to control idle. hope I am doing ok
Okay thanks your doing pretty good I think. Like I said I'm a noob and trying to learn what I can. I'll fix that in the tune. Thanks for explaining it tho.
Closed loop idle RPM control doesn't happen until you get
to the warmup temperature that's specified in that tune
parameter (Engine>Idle>Adaptive Idle RPM > Min ECT.
On my Vortec van this is 176F. With a cold 'stat you
might just never get there. In winter with an iron block
it might just take a while. Takes my iron block van about
2 miles to warm up at a 30MPH crawl.
Oh so your saying when it goes it to closed loop it's commanding a different idle speed? I mean that makes sense if so because after the engin warms up and you restart it, it will be and 600 and in about one min it climbs up to 700.
Off topic here but when I start the engine in the morn when it's cold. It runs like poop, by the wide band it goes way lean When I give it the gas and then comes back. But evertime I give it the gas it goes lean until it warms up a little then it's fine and drives good.. Is this another open loop problem?
There's closed loop (AFR) and there's closed loop (idle RPM).
Also called adaptive idle RPM. They work on different things
and they have separate enable ECT setpoint fields. Until it
(idle closed loop RPM) is enabled, you're running off the airflow
numbers and the motor's efficiency changes as it warms up
so RPM will change as well, even if incoming airflow is held
constant (but generally desired airflow also has some ECT
profile, which if tweaked might be semi-stable but as stock,
or modded and untouched, maybe not.
There are also various after-start actors which fade out
as you describe. You may see them as AFR adders if you
add these to the scan PID list. There is also a time delay
in addition to the ECT threshold, for closed loop (adaptive)
idle to begin. I think I saw 0.8 sec, well less than your minute-
range observation. That one may be ECT getting right (the
radiator water may have cooled below threshold even when
warmed up and then stopped, and need to re-climb a bit
as it starts to circulate into the block again).
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