Iac ?

[IrvJr]

What is the IAC supposed to read at idle? And what does it do when accellerating? I have a feeling mine is going bad but i dont know what it should be reading. It reads 0 at idle but when i give her some gas it goes up alot, comes down very slowly and drops to zero. My idle has been surging too, related, i dont know. But the chip is a Thrasher 97. It says the programmed idle is 697, isnt that too low. And the o2's at idle are 830's, isnt that high for idle. I thought it just bounced around at idle and didnt stay at one particular reading til WOT.

Help, Scott

 

[scottyb]

Scott,

Your IAC is not a sensor. The number you see is the "amount of command" the ECM is "issuing" to maintain idle. The higher the number, then the more work the IAC is doing to maintain idle. If the number is 0, then the ECM is not commanding the IAC to open in order to keep 750 rpm. Basically, you have no "control" over the idle speed and it likely is over 750, and jumpy. You want to close the trottle plate via the set screw to get the numbers up. You want numbers about 15 to 30 or so. Usually a vac leak will cause your problem. Remember to go thru the TPS set procedure in conjunction with IAC adjustment.

As far as IAC at cruise, I'm not sure it is a significant number. I don't see any use in the IAC when driving, but I may be wrong.

Scott

 

[bruce]

The IAC,
tries to maintain a commanded idle speed.
Has a throttle follower function, it adds steps as you crack the gas open, and then when you lift fast, it holds the revs up just a tad to prevent stalling.
It boots the idle for when the A/C is on
It gives extra air when the engine is close, for part of the choke function.
I forget off hand it adds some counts for the Radiator fan or not.
Then has a stall saver function, so the engine doesn't stall. Well tries to prevent stalls.
The idle control involves ALOT of code. Like 25% of the code in the ecm is just for the IAC.

 

[IrvJr]

So is it working correctly from the info i have given, and should i be looking for a vacuum leak?

Scott

Thanks for the input.

 

[Spooled85gn]

IAC PROBLEMS.....

My IAC count in park is 89. I've tried upping the idle to get it to lower, but it raises as the idle goes up.. The idle is at 1k all the time, and the set screw is backed out completely. The idle varies a little bit 950-1000 rpm. TPS is .46. What could be the problem... Its running and driving quite well, we even just converted the LS1 MAF to "blow through", which I strongly suggest. My mods include, Translator, 009's, EGR tower removed/filled, gasket matched ports, stock headers, stock turbo till we figure this bs out, 3" integral dp, underdrive pulleys, adj wastegate, Comp 212 cam... HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[BoostKillsStres]

Spooled85gn

If you have the set screw backed out all the way so the throttle blade is completely closed, thats why your IAC numbers are so high!! With the blade all the way closed the ecm isn't seeing enough air to reach the chip commanded idle so it opens the IAC valve to get that air. As you open the throttle blade using the set screw on a fully warmed car, you should see the iac count begin to drop but you must also make sure you dont go over 0.48V on the tps in this process as the ecm will then think you are off idle and things will change.

You didn't say how you tried to up the idle as that is only controlled by chip parameters, not by the set screw, thats only to establish minimum air for the engine so that the ecm can then control idle using the IAC for varying load conditions such as A/C and fans coming on and partial off idle transitions and even lite cruise.

You may want to pull the IAC valve and attack it and the passages in the throttlebody w/ o2 sensor safe cspray cleaner to make sure things are clean and the IAC valve can seal properly.

There is also an IAC reset procedure on gnttype.org but I haven't found the need for it as long as you can monitor IAC counts w/ a scan tool and adjust properly.

Good luck,
HTH

 

[Spooled85gn]

IAC

Thanks for your reply...
I've tried turning up the idle with the screw, but the iac counts only climb.. I think you're right about it sensing "non idle" when Im turning it up. I wasnt watching the tps.. Stupid me.. So I should raise the idle adj the tps once and a while to make sure its at .45? I followed the proceedure on GNttype, but like I said it says turn up idle till IAC goes into range, then set tps.. It doesnt go into details.. Let me know what you thing... Thanks

Mike

 

[83ttypecooled]

IAC

Hi!
Idle IAC should be low, about 11-20. In your case, you have too much closed throttle airflow, either a leak, as has been suggested, or misajustment of the base idle. When motoring down the road, 150 is common, as the ECM is ready for throttle closure at any time. Even our old systems act FAST, so the stepper motor can go from 255 to 0 in a second. TPS is vitally important, must be around 0.40 closed. It all works together, throttlebody MUST be CLEAN! Find a shop manual, set it to specs.
Good luck! Easy, when you've done it a few times!
Dale

 

[IrvJr]

Why is my IAC count at zero at idle? Is my set screw out too far?

Scott

 

[Ormand]

Irv, if you have a "zero", the screw is IN too far, not out too far. Turning the screw IN gives more air, does not change idle speed. If the screw is in too far, the butterfly lets too much air pass, and the IAC goes fully closed... to zero. If the screw is out too far, the butterfly will be closed, and the IAC will have to open wide to get enough air, giving a high IAC number. But neither case will affect idle speed. The GNTTYpe directions, taken from the shop manual, are good only for the stock chip, or an aftermarket chip with the same idle settings. Many aftermarket chips use different idle settings than stock, and the 500 rpm may not be right.

 

[IrvJr]

My idle speed says 667 on the Direct Scan. Is that the programmed idle? What about the slow return to idle? it slowly creeps back down, once in a while it will go down a little quicker. Bad IAC maybe?


Scott

 

[seeyabye]

Remember that after you make adjustments to the IAC, you must turn the car off for a few seconds, then restart. Make sure that after you adjust the IAC, the TPS voltage does not go over .48 at idle. If you turn the screw in, you should see the idle raise. Then turn the car off for a few seconds and restart it. the idle will be lower as the IAC is able to monitor the airflow. Keep making adjusments until the IAC is where you want it, remembering to keep the TPS adjusted.

 

[IrvJr]

Does the TPS change as the IAC changes? My TPS is set at .44 and has not changed yet. It is idling better but not perfect, yet.

Thanks,
Scott

 

[BoostKillsStres]

TPS does not change with IAC only with screw adjustment or movement of throttle arm.

 

[83ttypecooled]

base idle

I think that 500rpm is pretty much a good starting point when we're talking about this problem. There are a few rules of thumb that one may use, and this is an example.
When the vehicle runs at 500rpm, all timing is at base and the thing is in swinging **** mode, so to speak. What better time to nail down the situation?
Dale

 

[Spooled85gn]

Thanks

Thanks for the reply, It's still not working as planned... IAC wont go under 60.. we keep setting the tps.. but IAC is still up at 60.. Any more input?

 

[Razor]

Laymans terms..

To raise your IAC number, close the throttle blade.

To lower your IAC number, open the throttle blade.

You open or close the throttle blade by using the screw on the top. Do adjustments one half turn at a time, and then wait patiently for the ecm to "relearn" the new setting.

Every time you make a 1/2 turn adjustment, make sure your TPS is still within the .38-.46 numbers.

So Irv.. your IAC is at zero becuase your blade is too open. Close the blade 1/2 turn and perform as I describe. Dont pay attention too much to the programmed idle on the DS. Just make sure your at "some number" greater than zero. If you close the blade and still have zero IAC, then you have a big vacuum leak. look at your BL's at that point.

Easy

 

[Spooled85gn]

Thanks

Thanks for the reply.. Now my problem is that the RPM is at 1050 at idle. The IAC is now in spec at 18 and the tps is .46... Why is my idle still so high.. To know what I have in the car as for parts look at one of my first posts in this thread.. Thanks for anything you guys can come up with..

 

[IrvJr]

My BLM's are always around 128. I have looked over and over for a vacuum leak and none found. But i did close the throttle blade some and it runs so much better. The idle is smooth and back around 800, sometimes i think the car has stalled it runs so smooth. Now help me sort out my part throttle knock.

Thanks Guys,
Scott

 

[Razor]

Re: Thanks

Originally posted by Spooled85gn
Thanks for the reply.. Now my problem is that the RPM is at 1050 at idle. The IAC is now in spec at 18 and the tps is .46... Why is my idle still so high.. To know what I have in the car as for parts look at one of my first posts in this thread.. Thanks for anything you guys can come up with..

drop your tps to like 42 and drive the car for a little bit. Now put it in park.. what does the IAC read. If the IAC reads like 20 and the car is idling 1050, then the chip is telling the ecm to idle the car at 1050.

Change chip.