Haans249

iTrader: (24)

Hello Everyone,
I've been having some idle transition problems, its been worked out pretty well, but the last thing i've noticed when its doing this is my IAC valve count goes down to 20 or less and then it'll stall, or if i give it gas it'll pick back up. Only thing is it does it everyonce in a while.
My question is, what should I do to increase my IAC counts at idle to like 60 or so?
Also, how does the step relate to the actual position of the IAC valve. Does a count of say 300 mean its opening the passage up all the way (the valve moving all the way into itself) or does it mean its moving all the way out closing the passage? It seems to me that something in my tune is causing my IAC valve to want to move to super low values, sometimes even as low as 3 or 4, and causing it to die due to lack of air (checked my AFR values at these points with my LC-1 and it goes rich, meaning lack of air). What in my tune could be causing my IAC valve to act this way? I've got everything dialed in on my tune, VE table dialed, RAFIG, sparks, learning, ect... Its gotten a lot better, but this last thing I can't nail.

Mods
228/236 on a 112
FAST 90/90 tb
Powerbond 25% UD Pulley
ARE Stage 3 heads
Edelbrock Stepped headers
ECT...

Using EFILive and I'm running OLSD tune right now.

Best Regards,
Adrian

Haans249

iTrader: (24)

Biggest question I can't find an answer for is....

At a count of 300, what is the location of the valve? Does 300 or so mean that the valve has moved all the way out of the motor? Or does a step of 300 mean the valve is pulled all the way into the motor? Right now, from what i've been figuring, the higher the step, the further out of the motor the valve will move, and a step of 0 the valve is all the way in, opening up completely the IAC passage.

Thanks,
Adrian

SSpdDmon

iTrader: (10)

From my understanding, the IAC steps max out close to 360. However, the desired idle airflow table only goes up to 310. The greater the steps, the more the tb blade is open. Ideally, you want this number to be between 60~100 at a steady, warm idle.

I would suggest using the bi-directional controls to find a good idle point (close to 850rpm should work) as well as a good idle spark advance (try adding a couple degrees). Then, go into the desired idle talble and base spark tables to adjust the values at idle (need to pay attention to GM.DYNCYLAIR_DMA & RPM to change right cells). You may need to tweak the IAC Effective Area for the 90/90, but I thought I read somewhere not to mess with this table and to just make changes to the Idle Desired Airflow. This is where things get a little fuzzy for me...

Once you get it close enough to run on it's own and assuming you have the latest version of EFILive, log the ECT & RAF pids (and their supporting pids - right click 'More Info') from a cold start. They will take the sum of the LTITs and the STITs, which is what you use to fine tune your Desired Airflow Table.

There's probably a few other things that people can chime in on to help you further (or hopefully to correct me if I'm wrong). I'm still trying to figure out if adjusting the set screw or drilling the throttle body has an effect on the IAC Effective Area table and if so, how much.

Haans249

iTrader: (24)

Thanks for the reply! But I have already gone through that procedure. What I need to know is literally the position of the valve when the steps are at 300 and at 0. At 300 is the valve all the way out, closing the passage, or all the way in, opening the passage all the way? Maybe I can use the Bi-Directional controls when the engine is off and pull my IAC valve and see what it does.

Thanks,
Adrian

Haans249

iTrader: (24)

Hey, so it turns out that this is incorrect. I finally went outside and used bi-directional controls, when engine was off, and the IAC valve out. I set the step to 127, and wala, the valve moved all the way in...opening the IAC valve passage. Back to 0, and it moves out, closing it.
I also went ahead and opened the throttleplate with the set screw, reset TPS/IAC, and then flipped the engine on.....it did exactly what I thought it was going to do, and that was the steps went straight to 0.

SSpdDmon

iTrader: (10)

That's what I get for assuming. I thought the IAC actually moved the tb blade. So your saying it's a valve that moves in & out and breathes through one of the holes in the top of the tb?

Haans249

iTrader: (24)

Nope, the IAC valve is just that, a valve =D. On not ETC vehicles (camaro/transams) the idle airflow is controlled by the motor that plugs into the side of the Throttlebody which moves the valve in and out, opening and closing the passage respectively.

Best Regards!
Adrian

BADSZ28

iTrader: (39)

Where is it getting the air from though?

BADSZ28

iTrader: (39)

How do you lower IAC?

SSpdDmon

iTrader: (10)

I belive the air comes from that funky part inside your TB that people epoxy in when they port & pollish. That explains why some have idle issues after a TB install. Not enough air flowing to the IAC valve.

To lower IAC's, you can either turn the set screw under the bump stop on the TB or drill a bigger hole in the TB blade. Either way, a little tuning to the IAC table and desired airflow table (RAF) is needed.

Haans249

iTrader: (24)

Well, you do need to tune your desired airflow table, but definitely don't mess with the IAC valve calibration, that'll screw stuff up.

But like he said, and what I discovered, that the larger the IAC count, the further inside the plunger goes, hence opening up the passage more allowing more air, the smaller the number to 0, the plunger is all the way out closing the passage. If you want to reduce your IAC counts, open the throttle blade more via set-screw and reset your TPS.
Although I do have to say, that you want your IAC counts to be 60-80. If its too low, then you'll have stalling problems when coming to idle if you have a cammed vehicle. Also, the IAC position will change based on your LTIT and learned idle airflow corrections. So, really changing the IAC position really is quite difficult haha.

Best Regards,
Adrian

DirtyJohn

iTrader: (8)

Don't know if this helps or not, or if its correct, but this is taken from page 102 of a link I found in one of the "getting started tuning" threads.
Not sure of the link, but the entire thing is a good read.

Haans249

iTrader: (24)

Thats a really good rendition, except the cutaway pic is wrong, the opening of the throttlebody needs to be facing outward, not to the sides, but none the less I htink people get the general idea.

Best Regards,
Adrian