to clear up the idle tuning questions about IAC

[S2H]

I was talking on the phone last night talking business with KEN...and we got around to discussing the Idle tuning issues....

STOP changing the Idle set screw and resetting TPS....
STOP moving your IAC effective area table.

the proper way is to get your IAC counts down by drilling a second hole...start out with a 1/16 and slowly work your way up to an 1/8 in 1/32 incriments......
this is because of the way the pcm calculates things and the tables that have fixed values because of being a formula and not a table

then you need to do an IDLE RAF and get your Running Airflow to be the right values.this is the primary thing to fix idle issues..other things effect it...but if RAF is not right...you are pretty much screwed

after that you need to look at the spark adders for overspeed and underspeed as they are usually the culprit of surging and dipping....

also making sure your Idle spark and driving spark are not far off will help in the transitions as you are coming to a stop or starting to move..

[Chris@HPTuners]

THE MOST IMPORTANT THING

Allow your LTIT to relearn after making any changes to the RAF table. This can take 5-10mins for in gear and P/N.

[S2H]

LOL...forgot to say that....but I'm also used to doing RAF and its just part of it to me...

[jimmyblue]

What about the case, that you in fact -do-
have a different area profile with IAC plunger
position?

For example, I have a ported & filled TB, I know
for a fact that my maximum cross-section in
that passage is -well- less than the 0.5 inch
diameter that the max value in my stock table
indicates (did the arithmetic on that, at one
point). Yeah, I get a little surging, no, I didn't
mess with it (that). But it's definitely a point
of unrealistic data, in the system. Should I
clip the effective area to the -real- area-choke?
What would happen, if the "desired area" (which
I figure, the desired airflow computes?) is more
than can be had? "Can't get there from here",
as it were?

[S2H]

KEN explained to me that it has nothing to do with the passageway....its the IAC Motor pintle....and if you have th esame IAC motor..then it shouldnt change

[S2H]

also I believe that there is a table called "Desired IAC Area Max"....that you can edit...I know on an F-body its set to 84....this to me would seem like the place to "clip it off" if you have made the passageway smaller because of porting the TB and filing the IAC passageway square hole..

[MeentSS02]

Guess that would make sense why messing with all of that crap never netted consistent results.

[checkmate]

Guess that would make sense why messing with all of that crap never netted consistent results.

That is strange, this did help mine. Of course it is ported and polished so I'm sure that made a difference.

[S2H]

makes no difference on the IAC table...its an IAC Motor Pintle measurement....
same IAC motor...no table change

[MeentSS02]

That is strange, this did help mine. Of course it is ported and polished so I'm sure that made a difference.

Mine is ported/polished as well, and it just wasn't consistent. Leaving the tables stock and fixing my RAF table is the only thing I have been able to actually count on.

[jimmyblue]

KEN explained to me that it has nothing to do with the passageway....its the IAC Motor pintle....and if you have th esame IAC motor..then it shouldnt change

That's only true, if the IAC "orifice" is the smallest
area in the air path. If there's a smaller choke-point
then the maximum airflow area -has- been changed.
After the IAC "orifice" becomes larger than that the
IAC is not in control. If it's told to go bigger, it will,
but nothing will happen and this kind of thing is
prime oscillation material (surge).

[Casey]

That's only true, if the IAC "orifice" is the smallest
area in the air path. If there's a smaller choke-point
then the maximum airflow area -has- been changed.
After the IAC "orifice" becomes larger than that the
IAC is not in control. If it's told to go bigger, it will,
but nothing will happen and this kind of thing is
prime oscillation material (surge).

Correct.

I have not seen every single throttle GM made. As far as I can remember the the head of the pintle/orifice its closing is the smallest part. Most of the ones I have seen are a large passage way leading to the 1/2 orifice. Whats after that depends on your manifold/gasket design.


Most of the surge I see is from the idle over/under speed spark advance.
Also some motors (large cam) can never meet the proprotional/intergral deadband values. Raising them slighlty will keep the IAC from becoming overly busy.

Ken

[S2H]

That's only true, if the IAC "orifice" is the smallest
area in the air path. If there's a smaller choke-point
then the maximum airflow area -has- been changed.
After the IAC "orifice" becomes larger than that the
IAC is not in control. If it's told to go bigger, it will,
but nothing will happen and this kind of thing is
prime oscillation material (surge).

desired IAC Max takes care of that...you are telling it that you have too small of a hole and it stops when it gets there...in which case you need more air somewhere else...like drilling a hole in the TB....
and if you are far enough up to need that much more from IAC then you need a hole anyways...
filling the TB passageway has not proven to get any gains so if you filled and made a smaller passageway then you shoud consider making that a bigger hole so you dont max out the IAC max table first

the stock setting of 84 looks like it correlates to 199 steps....well above where I should be....I personally have only seen the high point on cold cold starts get up in the 160-190 area..so its seeming to match that # anyways...lower that table and it will never go above what the IAC table matches....

when it starts to oscilate you should reduce the amount of spark adjustment that the overspeed/underspeed tables do...as they are usually the primary reason for Ilde oscilation


Just so you know...this stuff was even hard for me to stomach teh first time I heard it...but now that I have heard it and tried it..it seems to make sense..and seem to give drastically more consistent results when tuning large cams...small cams sometimes just a little timing at idle and a little correction of RAF is all thats needed...Larger cams need attention to the other idle parameters....


also by the way.....
ETC vehicles do not have the IAC motor issuesCause they dont have an IAC Motor) and they use opening the TB blade to get enough air...and they know the difference between TPS and pedal...where cable drive is all pedal.....and tps and actual pedal are directly related on cable drive

[WS6FirebirdTA00]

havent quite read all that but i dont see why you dont want to adjust effective area, ill try to read through for an explaination. i have no issues with mine with adjusting it, actually the car runs better. effective area is the area seen for open airflow for a given iac step, this should mean that at idle the car should have a good grasp of how much to move the iac motor to allow certain airflow. so this should mean that the desired idle air and dynamic airflow curves should be parallel to one another. however you do not know how much air passes through openings in the tb by the blade and what not so i set them to overlap and the RAF might be high by a few g/sec. i see no ill side effects on my car at all, and this was also a huge help in drivability on many cars.

[WS6FirebirdTA00]

i should also say that i did leave the stock table in there and try it that way and saw no change for the better. what calculations are done with that table besides just the computer determining how much to open and close the IAC? or is that it

im not trying to say i am right or you are wrong at all, just want to see into this a little more and figure out is you shouldnt chagne it then why it helps out? just looking for strait facts

[S2H]

this is a post I made on ls1tech

Quote:
Originally Posted by Dixit
I cant remember or know off hand if the OEM LS1/LS6 ETC 78mm TBs come with small holes or not. But when I removed my ls6 intake/78mm tb setup, it has a good 1/8-3/16" size hole for the cam I got. Now the LS2tb I have which was ported has no hole and no slot on the side of the TB like the LS6 tb had. I managed to just adjust my ETC scaler and have no problems, the idle sits at 900 as I have it set, I can go from 7000rpm and hit the clutch and it stops right at 900rpm all the time. Never have idle hunting issues. Im not saying I have luck. But I agree with Chris, if you dont let the LTIT learn it will hunt around for awhile as it did in the beginning. Once I got my LTIT learned and as close to 0 as possible, its never given me trouble.

Dixit



as far as ETC vehicles are concerned.....its all about RAF...
you get RAF correct..and you wont have to mess with the ETC scalar at all regaurdless of cam size....
all you really need to know is that your idle is fast enough to make it so that the cam doesnt choke on its own exhaust gasses because of reversion from overlap
after that any dipping and surging you might experience is all spark issues..usually the overspeed and underspeed tables...
just reduce the amounts of spark they command...try it on a car that has some idle dippig issues after doing RAF and watch the problems go away


Quote:
Originally Posted by MNR-0
You can open the TB bump stop screw up till 0.63v without entering non-idle trim cells and is infact what I did to bring my IAC counts down. After retuning my base running airflow and tweaking the throttle cracker, it idles purrfectly and starts up with no idle flare whether its cold or warm.

IMO opening the blade is beneficial in that there is less motor control needed by the IAC, and provides a bigger holeshot of air for a stable return-to-idle.

As long as your IAC counts are around 40-60 at ilde, adaptive idle advance is switching around 0* as closely as possible and your VE map doesnt have large variations around your idle MAP (45-60 and 800-1200RPM) I cant see why you would have too many idle problems.

Some TBs have issues in that their CAD design did not take into account the large IAC rear breather hole needed on our V8s. Usually, though, a dremmel will fix that.




I asked ken about this too...
Quote:
Originally Posted by soundengineer
I understand that after a certain TPS it gets into no longer being Idle cells....
something like.62 volts or something around that amount....or something like that..LOL

Quote:
Originally Posted by KEN @ HP Tuners
That is the exact reason to leave it alone. There are over 5000 parameters in the VCM. Not everything you can adjust that sees the TPS is in the editor.
You will just wind up screwing things up.


__________________

[S2H]

i should also say that i did leave the stock table in there and try it that way and saw no change for the better. what calculations are done with that table besides just the computer determining how much to open and close the IAC? or is that it

im not trying to say i am right or you are wrong at all, just want to see into this a little more and figure out is you shouldnt chagne it then why it helps out? just looking for strait facts

by changing the table you are in effect telling the pcm to respond more with spark and less with IAC...as most of our IAC's are just too slow to respond properly....
what happens is that you get both the slow IAC response and teh fast spark response figting each other...IAC commands 5 steps...but timing commands +12 degrees before it can get there..causing overshoot...then they both command the other direction...

by changing the #'s all you have done is commanded the pcm to use more spark movement and move the IAC less

I wish I could tell you the other stuff that it can mess with...but I'm not the creator and I dont want to pick apart a PCM from scratch with my little bit of programing knowledge...

[WS6FirebirdTA00]

so are you talking about spark changes at idle? cause with the stock effective area in there my timing swing was no different. comming to a stop or free reving the motor, the rpms come right down to desired without over or undershoot at all. since i fixed that lean problem at idle, my idle stays pretty steady, largest rpm change i see is 50 rpm total, 25 over or under desired and thats with head and cam. this is also with the stcok 01-02 over and underspeed spark tables. only difference i can tell is with the modified effective area table in the computer the car seems to be under better control of the rpms. just out of curiosity, have you ever tried and compaired to see a difference?

[S2H]

yes...which is why I posted...
if your RPMs swing you usually need to adjust RAF and overspeed/underspeed spark advance tables

[MNR-0]

Well then, why is the bumpstop there in the first place? Its adjustable for a reason.

I personally wont drill out my idle hole unless its absolutely necessary. I want to keep things stock.