Idle Tips & Tricks

[Redline Motorsports]

How do we "properly" calibrate the IAC effective area when making a change to a 90mm TB?

[white01ss]

How do we "properly" calibrate the IAC effective area when making a change to a 90mm TB?

Maybe copy or interpolate the data from a stock tune that has a 90mm? I would think the flow rate shouldn't change too much because IAC effective area has to do with the flow of the idle air circuit at various IAC motor steps not the size of the throttle body. As long as the idle air passage is the same size it should be real close to the 78mm TB data.

[tinindian]

How do we "properly" calibrate the IAC effective area when making a change to a 90mm TB?

Sorry to bring this up again, but I have the same question about IAC area with a 90 / 92mm TB. What cars / tunes would have a 90mm TB?

[Rich Z]

Sorry to bring this up again, but I have the same question about IAC area with a 90 / 92mm TB. What cars / tunes would have a 90mm TB?

I believe all the LS2, LS3 and LS7 engines in Corvettes (2005 thru 2013) have 90mm throttle bodies. Be aware that in 2009 there was a change to the TBs that seemed to affect WOT voltage signals, however. These new ones are identified by having gold or brass colored TB plates instead of silver colored ones.

[white01ss]

Are there any stock vehicles that came with a cable operated 90mm TB? I couldn't find one. They all seem to be ETC (Electronic Throttle Controled) so they don't have an IAC module or passage to use as reference. I just upgraded to a 90 FAST and left IAC Effective alone. Had to tone down the Desired Air and throttle follower to get rid of some hanging idle when hot, but other than that I really didn't have to do much.

[tinindian]

How do we "properly" calibrate the IAC effective area when making a change to a 90mm TB?

For my 92mm NW TB - I did some reading and found I had to map Desired Airflow B4307 vs. ECT and also Desired IAC Airflow (IACDES_B) vs. ECT. If the two tables don't match during warmup you need to offset the entire IAC Effective Area table B4403 up or down, re-flash & map until they do match. It took about 3 tries but I finally got it right - ended up offsetting the table B4403 down about 5 cells. My stock tune had zeros in the top 7 cells (0 thru 12 sq.mm) and now I have zeros in the top 12 cells (0 thru 22 sq.mm). I was amazed how much better the car idled and driveabilty is a little better too. I guess the PCM works better when actual airflow = calculated airflow LOL.

[SOMhaveit]

IAC effective area does not change on a cable throttle body. You use the same idle air control valve on the 90mm TB that you used on the 78mm TB. It opens the same amount for the IAC counts and allows the same amount of air in no matter the size of the throttle body. What does change is that you can get more air around the throttle body blade because it's larger. It should be all about RAFIG when you are cable-driven.

[SOMhaveit]

For my 92mm NW TB - I did some reading and found I had to map Desired Airflow B4307 vs. ECT and also Desired IAC Airflow (IACDES_B) vs. ECT. If the two tables don't match during warmup you need to offset the entire IAC Effective Area table B4403 up or down, re-flash & map until they do match. It took about 3 tries but I finally got it right - ended up offsetting the table B4403 down about 5 cells. My stock tune had zeros in the top 7 cells (0 thru 12 sq.mm) and now I have zeros in the top 12 cells (0 thru 22 sq.mm). I was amazed how much better the car idled and driveabilty is a little better too. I guess the PCM works better when actual airflow = calculated airflow LOL.

Actually, after thinking about it, this makes sense. What I have thought was correct may well be incorrect. That calibration must be taking into account some air coming either around the TB blade or the factory hole in the oem TB, so a larger TB with more air coming in around the TB blade would have more idle air entering the intake, so 0 steps on the IAC would be more square mm.

[samh_08]

How about MAF-less tunes? Any alternatives to RAFIG/RAFPN?

[Aint Skeered]

i just went for a drive and got a good data log. only surging I'm getting now is when I am going up my drive way off throttle but moving slow. my question is do I copy log then pate and multiply this in my tune or how do I apply the logged values?