Just to clear it up. It's motor steps. Minimum value is zero, max is 340. So 30 steps is roughly 10% open, but by airflow it's a slightly logarithmic curve, not linear. There's a calibration table to tell the computer what step equals what area

 

there we go, thanks dude. so 20-30 steps is an ideal target, around 10% open is great for most engines. If followed, my procedure nets this behavior if you are able to do exactly as I have it written.

Mildy curious, where does the airflow begin to taper, I bet around 50% it flattens out.

 

IAC count of 30 is very little airflow and will lead to a car with an unstable idle. On most tunes, counts 1 to about 15 or so have 0g/sec airflow. Most shoot for 60 to 80 counts warm. Somewhere near 200 you get very little additional actual airflow because the inlet is smaller than the wide open orifice.

Also, your procedure still won't work. You need to be logging IAC counts and airflow. Period.

 

You are telling me that 7% additional area at the IAC valve gives 0% additional airflow total? I call bullshit. My figure of 10% means 10% open. It doesn't mean 7% of nothing and then 3% open, it means 10% opening total. so if the first 10 or 20 steps is still 0% then it does not count towards the 10% I am suggesting, since with 10-20 steps you are saying it is still 0% open. Please try to use common sense.

#2 when you disconnect the IAC it will take into account any baseline IAC setting opening, Since you disconnect the IAC at its lowest point, often this is as low as it ever was to begin with i.e. according to you, it was hovering around a minimum of 50-60 steps to begin with, or more, and once disconnected cannot adjust below that point by the computer. In other words, if the idle was too low to begin with, it had to be with a minimum of 20 steps, because anything below that means 0%~ additional airflow according to you. So when you set the idle just below desired speed it is also using whatever that flow amounted to for it's total ( which according to you is 0% additional airflow) it will be 20+ Whatever your computer had to add to get it back to desired idle speed. You will be able to tell right away if the idle is too high for some reason after plugging in the IAC, as this is the only possible negative outcome of my procedure if you are not 'tuning' the vehicle simultaneously and able to watch the IAC movement. My post is directed towards those individuals without tuning experience or knowledge so that they can get their IAC just really CLOSE to the ideal setting without touching a laptop. Of course it would help if you can command things manually, but typing to the op "go into the laptop and command the IAC to a low step count so you can set the idle" wasn't going to work.

"unstable idle" doesn't make any sense. You dont need an IAC for a 'stable idle' once the engine is warm. The IAC adds air for cold situations where the engine might bog, and it helps set the throttle down gently to keep the engine from under-running. Idle stability is more in the hands of the computer, camshaft, timing, and a slow rate of IAC compensation if the engine is a radical performer. It has nothing to do with the number of steps we use; you can remove the IAC all together, drill a hole in the TB and set the idle while warm and it will be fairly stable there at that temperature. You don't need a tps. Heck you dont even need a computer control, it can be carb'd. The reason I shoot for minimum steps is already mentioned: it helps keep the engine from bogging when the ECU is incapable of recognizing a large negative rate of change in the tps to compensate, and when the engine has a lightweight rotating assembly this is important that you get the number of 'steps' as low as possible.

 

Another way I can show what I am saying.

Imagine your IAC is clogged up. Imagine its got gunk in it, so that for the first 0-30 steps, there is no addl airflow. Kind of like what you are suggesting already.

So, my procedure has us disable the IACV at its lowest point. Lets say that is 0 steps. So you get the IAC to 0 steps and disconnect it completely.

Now, you set the idle just below desired minimum. You desire 850? Set it to 800~.

Now plug the IAC back in. What does it do? It will "see" you desire 850, and note the current rpm is 800. SO it will begin stepping out yes? It will step first from 0->1, and then 2, and then 3, and so on. Remember the IAC was clogged right? So it will step all the way through from 0-30 without ever raising the idle at all. And guess what? It will keep going! The ECU is trying to raise the idle! so it will continue stepping from 30+ until it finds 850rpm.

Now, lets say the IAC wasn't clogged. Lets say that from 0 steps to 5 steps is 10% addl flow. Guess what? The IAC will do exactly the same thing as before... gradually opening until it finds the 850rpm, regardless of how many steps it takes.

The whole point of the procedure is to keep the number of open steps to a very low minimum, something very close to baseline "0%" (wherever that 0% is, 30 steps, 0 steps, w/e it can 150 steps if the IAC is severely clogged). The less open the IAC needs to be for a hot idle the more stable the idle will be! Less movement = less chasing = better control system steady state! If your computer lacks the features necessary, that is.

For example if you lift your foot at 5k and the tps goes to 0% the computer should "think" we are returning to idle. It checks the engine speed, whoa! 5k! better close that IAC! if you had the IAC set to 150steps out at idle, and it starts to close at 5k, by the time you get back around idle speed the IAC might be too far closed, the engine rpm will dip down, perhaps even stall, as the computer freaks out and starts stepping the IAC back out to bring it back to 150 steps, which can take forever in some IAC motors, especially if you have it programmed to move slower. IF the ECU is incapable of recognizing those kinds of situations, or the tuner is incapable of programming an algorithm for them, then the safest/easiest/simplest way of preventing them is by the procedure I have provided which limits the minimum IAC position to some smallish number, thereby preventing the under-run situation I just described.

 

Tal0n, I posted a bit more comprehensive response in the other thread, but 30-60 is a general consensus for ideal IAC counts at warm idle. I've seen others say 60-80, but then if you're at 50, they'll say don't adjust it. I tend to try to get the counts to go lower as the cam gets larger. The controller HAS to be off the bottom in order to function properly or it cuts timing and fuel to maintain idle, resulting in poor off idle performance.

It's not always a matter of understanding the dynamics, which you do seem to understand. You also have to understand the controller and its logic. And the software by which it is modified/tweaked.

I agree going below 30 causes trouble. Would you agree that a lot depends on which throttle body you have and how big the IAC bore is? I find that when the IAC port is drilled out to 3/8", it does much better than some with smaller holes. On throttles with a larger IAC port, 30 counts is moving some air. On throttles with as low as 3/16" IAC port, 30 is moving about 1/4 the air vs 3/8" port. So, you have to know your components, IMO.

You are correct, the first 15 counts only changes effective area by 2mm. And if you're not logging counts, airflow, commanded air, and idle trims, you're wasting your time.

 

Absolutely matters which throttle body you have. With the OEM 78mm tb, tuning idle was simple and low IAC counts were ok. It was much more tollerant. My 102mm FAST is a finicky bitch. Lower counts give no flow and higher counts don't give enough airflow. I had to get it juuuuuust right with my medium sized cam to keep it from surging or dying. My motor is currently out being rebuilt, forged 375, and one of my side projects while it's out is to modify the IAC channel for better flow.

 

Lately I have been working on completing a few sets of Idle Air Confi's.

It has been very warm here lately, so up early AM's to get the coldest start in possible.

It's taking two am's to complete a set. (One AM for drive and another for park).
I cringe each day that someone will complain of the noise. (Exhaust rumbles echoing from garage)
If I'm not out early it warms out fast and the histogram starts at the next temp up.
The first three temp ranges I'll get in the fall/ winter.

With the weather slightly different each day I get different results and its frustrating for me.
I was expecting/hoping for the Histogram to populate the same numbers each run for each temp and be done in one run at this! (In Park and in Drive)
Shouldn't it do that? What are your experiences?

Here are the different results. (Each starting from from 20 C/ 68 F)

20/68 40/104 60/140 80/176 100/212 120/248 140/284

D 2.4 1.9 1.7 1.6 1.5 1.5 1.5
P 2.0 1.6 1.4 1.4 1.4 1.4 1.4

D 2.2 1.8 1.6 1.5 1.5 1.5 1.5
P 2.1 1.7 1.5 1.4 1.4 1.4 1.4

D 2.2 1.7 1.5 1.4 1.4 1.4 1.4
P 2.0 1.5 1.3 1.3 1.3 1.3 1.3

D 2.3 1.8 1.6 1.5 1.4 1.4 1.4
P 2.0 1.6 1.4 1.4 1.3 1.3 1.3

And lastly the Config I settled with:

D 2.4 1.9 1.7 1.5 1.4 1.4 1.4
P 2.1 1.7 1.5 1.4 1.3 1.3 1.3


A FYI that I'm just trying to pick up HPTuners. I have a Pro Version and no wideband just yet.
My truck is currently just sitting, not currently driven. So playing around trying to learn to improve my mail order tune. Back yard tuning lol.
It will be professionally tuned but I'd like to try the basics like getting it to breath/ idle well.

So far I'm very happy that I got rid of the vacuum leak. That caused start up flares to high rpm's and no more Cruise Control Effect!
FAST intake bolts replaced with OEM!

With the last config it seems to idle the best. That's where it's at.

My STIT's hover slightly around 0. Slightly - OR slightly + just depending...
That's in the temp range of 80 C/ 176F where the fans come on and off.

As for the LTIT's I give up on them. They are always -10 or so. Nothing I do will correct them.

Here are my mods to look at:

LS2 402ci - Mods & Info:

-1999 S10

-1999 Silverado ECU
-Mail order tune.
-MAP: 1 bar

-LS2 402 stroker
-LS2 heads
-Comp Cams - 918 beehive valve springs
-Comp Camps - push rods
-Callies Compstar - crank, 4340 steel, stroke: 4.000

-Callies Compstar - connecting rods - H-Beam/ ARP 2000 bolts
-Weisco - 4.000" pistons (forged alloy -8cc R/ Dome)
-Comp Cams - XER cam: 224 230 @ 114
-SLP - 160 thermostat

-Nick Williams 102mm TB (drive by cable)
-Fast 102mm intake
-4" intake tubing
-cone filter: 5.375" diameter, 7" length
-5 wire truck MAF/ IAT
-Metco valve cover breather (Just took off)

-LS fuel filter regulator
-Racetronix 255 fuel pump
-Ford green 42 pound injectors (48.5 pounds for LS1, LS2 with spacers to fit LS2 fuel rail)
-160 thermostat
-94 octane (While learning how to tune)

-BRP/ Hedman ceramic long tube headers, 1 3/4"
-dual 3" exhaust, stainless
-Magnaflow spun cats, x-pipe & mufflers.
-rear O2's tuned out.

-FLT 4L65E trans
-Yank 3600 stall
-3.42 gears
-8.6 Blazer rear

-Red Top Optima
-battery relocated to bed.

 

My tune attached.

 

Question.

When doing a cold start and viewing the idle trims in the scanner as the engine warms passing each temp range... Should the idle trims be at a near perfect 0? (Give or take a little - / +) after inserting the Idle Config values? OR is that in a perfect world?

I hope not lol.
I'm asking because mine aren't.

They are negative a different amount each day, maybe depending on temp?

Another issue I resolved besides the start up flares, vacuum leak and CCE and cold starts.
Adding 50 camshaft revs solved that!

That makes me a happy fellah lol.
Peddle starts drove me mad!

So right now the idle trims aren't perfect but at the temp it idles at they are decent. Starts up and idles well.

Lastly TPS %: 0, Volts: 53 and IAC counts: 60-80.

 

Sounds pretty good! So it sounds like the only thing bugging you is the constant -10 long term idle trim?

Effectively then your commanded air is showing lower than your dynamic air except it's perfectly steady and idling great?

There are three options:

1. Do nothing. If you're in imperial units, that -10 is pounds per hour or -0.17 pounds per minute.

2. In your IAC effective area table, you can copy the values and move everything four cells to the right. Very commonly done with larger TB to fix thecIAC calibration. Then when you log again, your idle trims should be closer to zero. Lots of guys will say move it right or ten cells to the right.

3. You can follow the "IAC calibration it's a must" thread, log your IAC vs airflow to figure out how far off the IAC effective area table is and adjust it more precisely. Mine was basically 16 counts = 1 g/sec airflow. I was off by 2-g/sec, so I subtracted 32 from the entire table.

 

Thx for your reply Darth_V8r,

Besides the long term idle trims all seems to be fine. I just disabled the LTIT'S (for now), as they were haunting me.

Will try out number two, moving the cells over and read up on number three. Right now number 3 is ahead of me.

 

Everytime you do the idle config it will differ a little day to day due to weather and humidity. The pcm will adjust accordingly as long as you are close. You can log stit for idle to see how much air it is adjusting.

 

Thx gagliano7 for the info.

I feel I have the hot/ cold starts good as well as idle. With long term idle trims off I'm more sane lol.

Fuel trims are decent but I need the ltft's on to balance things for now, until I can better adjust with a wide band.

My stft's are around +2 to -2 with the help of the long tern trims correcting things.
Not so steady with ltft's off.

The long term trims sometimes out of nowhere bounce to a -8 when the engine gets really hot and the fans kick but very soon after correct to good number. The short term is around 0 to +1 for the most part.

Love my HP Tuners!
I still have not upgraded to latest format, not sure that I will. Just getting familiar.

 

Not into having loads of gauges but realize the importance to have. Just like things simple.

I may one day grab an Aeroforce but for now just picked up a Scangauge. There are not a shitload of pids that my ecu picks up, but the few I am able to use like the trans temp is a bonus.

Glad my Tru-Cool 40k trans cooler is doing a great job.

The Scangauge is updating OK. Not slow like I read.
Just have to decide where I'm going to mount it. Hate clutter.

Like that Lonely Island video on YouTube, maybe I'll "Throw it to the ground!" LOL.