IAC effective area

[94SS]

Alright, I have been playing around with this I got the Idle Airflow values to match my MAF gm/sec. LT Fuel trims are -6 Bank 1 and -2 Bank 2. And desired airflow is like 6.7 gm/sec and MAF airflow is 12.5 gm/sec. You have to move the IAC effective area table over about 12 spots to get these values to match up at 12.5/12.5 gm/sec and IAC trims are 0. And the car seems to run worse with them matched up as if you don't touch them. Looks like what changes the most is with all that changing the IAC position at start 192 when real cold but on warm starts it is like 72 and it has a real bad cruise control effect. I am trying to figure out what I am misunderstang to getting everything lined up correctly. And what is the proper way to get correct gm/sec values for the IAC Park position vs. IAT I have moved them up and down and it doesn't seem to make a difference where you have them so I have left them at 21 gm/sec? Thanks.

[Chris@HPTuners]

The IAC airflow and the MAF airflow are not directly related. The MAF (in theory) measures the total airflow into the engine, thats the air going past the blade and thru the hole PLUS the air going around thru the IAC bypass system.

The IAC airflow is only the desired airflow that you want going thru the IAC bypass.

If you didn't change your IAC system in anyway, then it's best to leave that table alone.

Chris...

[94SS]

The IAC airflow and the MAF airflow are not directly related. The MAF (in theory) measures the total airflow into the engine, thats the air going past the blade and thru the hole PLUS the air going around thru the IAC bypass system.

The IAC airflow is only the desired airflow that you want going thru the IAC bypass.

If you didn't change your IAC system in anyway, then it's best to leave that table alone.

Chris...

How do you come up with the gm/sec values for the IAC park position vs. IAT or does it even play much factor in idle tuning? All I have heard is everything above 40 Degrees celcius make 21.

[Chris@HPTuners]

the park position is only used while the ignition is off.

[MNR-0]

I have found from trial and error its all Base Running Airflow for idle. Thereafter cruise effects and the like have to do with an incorrectly mapped spark table and VE MAP at very light throttle. After I installed my cam, I remapped the 0-0.24g/sec spark table to allow for smooth spark transients at light throttle which made the car cruise like stock again under all conditions. Its also wise to increase your MAP values for DFCO so as to enter into DFCO on decel with a cam. Otherwise the cam holds too little manifold vacuum to ever trigger it.

[WS6FirebirdTA00]

Chris,

when you scan desired idle airflow, you are saying that is only the airflow to pass through the IAC opening? Or no? My understanding of it was the desired idle airflow is the total airflow for idle. I have done quite a few effective area tables like this with great results. My take on it was the dynamic airflow should be the same as the desired airflow. If they are off at all then the effective area is incorrect and the computer doesnt know how far to open and close it for a certain change in airflow. I have tuned my car with and without the stock effective area table and it seems the one I made helped the car run much better. Plus when I left the stock one in there my RAF went down to 6 g/sec at hot idle but dynamic airflow was 10 g/sec. I just found it odd that with a cam the idle airflow decreased.

[WS6FirebirdTA00]

take a look at your throttle cracker table, i know mine was set at 3.0 g/sec and 1600-2200 rpm, setting that closer to teh rest of the table really helped

[chrisj6]

Mine was idleing and running fine when I got the spark tables smoothed out and the IAC counts down. I never touched the effective area tables and after my cam swap, i raised the idle only about 50 rpm (Z06 cam) and got the idle trims perfect, my IAC counts were 65-72 which is where you want them correct?

Chris

[WS6FirebirdTA00]

you want them at a hot idle around 30-50

[Chris@HPTuners]

Chris,

when you scan desired idle airflow, you are saying that is only the airflow to pass through the IAC opening?

yes.

[WS6FirebirdTA00]

interesting...

so that would mean that the running airflow is only the airflow for the iac and nothing else, just the air going through that particular opening.

i was always under the impression the idle desired airflow/base idle airflow was the TOTAL airflow not just going through the iac hole. i would think that if you set the iac to 0 with the controls and saw the airflow then, say 4 g/sec, that if the actual and desired airflows line up and you have the idle air table set up, that you could subtract 4 g/sec from the base idle airflow and then shift the effective area to get the idle trims back in line.

either way you look at it, the desired idle airflow and dynamic airflow lines in the graph should be parallel to one another from full open to full close of the iac motor. by the time its all said and done anything having to do with idle is corrected with the base idle air table. only thing that i would think would come into play would be returning to idle or the amount the iac motor is open when driving down the road.

[94SS]

Anyone have problems with IAC trims? I had -.5 in Park so I took out .25 from your Running Airflow Table and then it shoots to the max of LTIT .5 . What is the cause of this problem?

[Chris@HPTuners]

yes the IAC steps vs. desired area table would generally come from the manufacturer of the throttle body/IAC and not something that would be calibrated by the OEM guys.

The main things that are calibrated are how big to make the hole in the throttle blade so that the IAC dynamic range is not wasted (ie. thats why you should aim for around 50 steps at idle, but anything up to about 120 is ok i have found on 5.7L engines). The other stuff is the Base running airflow and then the Prop, Integ, Deriv RPM control stuff (also the idle spark control) that the calibration engineers just love playing with to get all the transitions fast but still stable. Then the main driveability is done using the follower/cracker depending on the trans type and application.

[WS6FirebirdTA00]

i disabled my cracker and get the best resulst with that, i thought that was odd

[94SS]

Is it possible to get rid of the brief 300 RPM drop that you get when you put a A4 in reverse with a good sized cam. I have been looking through all the tables and it don't look like there is anything for this even though drive and reverse are considered in gear but have different loads.

[WS6FirebirdTA00]

not sure ihave yet to mess with an auto, my car and all my friends are m6

[chrisj6]

if your idle trims are now .5, go to the conversion calculator and put .5 in the lb/min, and then it'll give you a g/sec amount to add to your base running airflow table for that temp range. It's best to log a cold startup so you can get a wide range of coolant temps calibrated to as close to zero as you can.

Chris

[WS6FirebirdTA00]

if its 0.5 lb/min then i bet the car runs like total ass, i dont think the limits let it get that high but that would me about 3.7 g/sec

[94SS]

Here's a good link that explained a little bit more for me.

http://www.hptuners.com/forum/showth...acker+settings

[94SS]

What effects do the first three columns of the VE table have on idle control if you are still using a MAF are they part of Desired IAC airflow? You would think since the MAF is still plugged in it would use data from the MAF table and the VE tables would not be able to create problems.