iac issues
iac issues we are trying to get a tune on my car. we cannot however get the IAC count down. We have a fast 90 intake on the car (00 ls1) and a ptm 90mm throttlebody. I know as the throttle plates are opened the iac counts should go down, and my experience with iac numbers ive seen them be in the 30s. We cannot get the iac numbers below 100 even screwing the throttle plate open which should ultimately make them go down. We also swapped another iac motor on the car and it did the same thing... It does move around but it goes from 180 or so and the lowest it has gone down to is 100. Do the iac tables need readjusted in the ecu, and is there a formula to calculate my new numbers?
TECH Fanatic
Joined: Feb 2004
Posts: 1,259
Likes: 0
From: Lexington, KY
Well I'm not the expert, but from my limited experience it's affected by airflow and timing. Sounds like it just needs more air, or perhaps your timing is way off. With more airflow, it should come down. And obviously you have to reset the tps sensor each time you make an adjustment to the stop screw. I had to adjust my throttle stop screw all the way until the tps sensor would not zero out anymore, and still had to drill a larger hole in the tb blade to get my iac counts to come down. But when I change the timing, it also changes the iac counts. I want to say when I retard it they go back up but that could be backwards.... It's a pain to get it right.
Well I'm not the expert, but from my limited experience it's affected by airflow and timing. Sounds like it just needs more air, or perhaps your timing is way off. With more airflow, it should come down. And obviously you have to reset the tps sensor each time you make an adjustment to the stop screw. I had to adjust my throttle stop screw all the way until the tps sensor would not zero out anymore, and still had to drill a larger hole in the tb blade to get my iac counts to come down. But when I change the timing, it also changes the iac counts. I want to say when I retard it they go back up but that could be backwards.... It's a pain to get it right.
we gave it more air, timing, and subtracted and went each and every other way, and the iac still damn near stays maxed out
You MUST back the throttle blade back to the point that it resets at zero. From here, you will have to begin to drill the TB for the extra airflow. The car will not idle properly if not at 0% TPS.
Thats bull. You can open the blade with the setscrew and then reset the tps from there by unplugging tps, turning ign on for however long it is(I usually just leave it on for a minute or two. Turn ign off and then plug tps back up.
-edit-
looking at your post again, you called bull on what I said without even understanding it...
Last edited by Frost; Oct 8, 2007 at 12:36 AM.
Trending Topics
It's the blade... Get the car up and running to a hot idle with the TB blade screw set as far as you can go and still reset to 0% TPS. Drill through the stock hole starting small (unless your counts are waaay high) and work up at 1/32" to 1/16" at a time and replace and check IAC hot. 50-60 usually works fine, but you can run it a bit lower if you'd like.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo TECH Fanatic
Joined: Feb 2004
Posts: 1,259
Likes: 0
From: Lexington, KY
It's not bull, I look at it every day. I SAID HE HAD TO MOVE IT BACK UNTIL AFTER RESET HE GETS 0%TPS. Once you reach a point 4-5% past OEM zero-point the TPS voltage will reach a level that is too high to be declared to 0% TPS and your reset procedure will leave it at 1-2-3%... whatever, as it's range is too high to reset. Idle controls are out of the window at >0%, so you MUST drill if you can't get the airflow by opening the blade. Only see this on large cam cars.
-edit-
looking at your post again, you called bull on what I said without even understanding it...
-edit-
looking at your post again, you called bull on what I said without even understanding it...
+1, drill the throttle body. Cant get some of em open enough without the tps not coming back. I dont even try anymore. Just crack the blade with the screw, and drill, and drill, and drill, til you get it right.
how big have these holes had to be, like i said theres already a small hole drilled in the blade, just trying to get an idea to when it might be too big because theres no going back.
so basically screw the throttle blade open as much as you can and get a 0 tps reading when you reset it, then just drill?
sounds pretty simple but want to make sure i get it right
so basically screw the throttle blade open as much as you can and get a 0 tps reading when you reset it, then just drill?
sounds pretty simple but want to make sure i get it right
There is SOME going back... start with your throttle blade open almost as far as you can get it and still get the TPS to reset to 0%; do this BEFORE you drill. If you overdrill, you back the blade back down a bit. You have a reasonable range to work with.
It's the blade... Get the car up and running to a hot idle with the TB blade screw set as far as you can go and still reset to 0% TPS. Drill through the stock hole starting small (unless your counts are waaay high) and work up at 1/32" to 1/16" at a time and replace and check IAC hot. 50-60 usually works fine, but you can run it a bit lower if you'd like.
thats the thing... the only way this car idles is if I keep it running... or the tb blade is open so far it idles at 2 grand
dude it doesn't matter... you can post about this all day but until you pull the blade and drill you aren't moving forward with your issue. Just take it out and start 1/16" over the factory hole... try it out and then rinse and repeat.
i understand that... just making sure i have everything else covered before i do this. Also this car is way rich at an idle. I had to rescale the injectors and my 36lb injector is actually close to 42 with ls1 fuel pressure. What do i need to do to the VE table to compensate for this?
i understand that... just making sure i have everything else covered before i do this. Also this car is way rich at an idle. I had to rescale the injectors and my 36lb injector is actually close to 42 with ls1 fuel pressure. What do i need to do to the VE table to compensate for this?
how big have you seen these holes have to be in the blade? ive drilled mine to about 8mm and it still is not down where the count should be. I adjusted the VE tables and the richness is gone, but at an idle at about 1000 it is still rich. I just dont want to drill this hole too big and its getting big already.
it is running ALOT better and actually keeps an idle athough its jumping around some. the IAC was maxed before, and ive gotten it down to 80 or so but at 80 if i crack the throttle blade open just a touch more it will go down to 30-50. ultimately i think the hole being just a touch bigger would do it, but im really leary of going past the point of no return.
i took way over half of my fuel out on the ve tables... i never dreamed it would be that much... explains why the plugs are screwed
it is running ALOT better and actually keeps an idle athough its jumping around some. the IAC was maxed before, and ive gotten it down to 80 or so but at 80 if i crack the throttle blade open just a touch more it will go down to 30-50. ultimately i think the hole being just a touch bigger would do it, but im really leary of going past the point of no return.
i took way over half of my fuel out on the ve tables... i never dreamed it would be that much... explains why the plugs are screwed
i agree... this is just the tip of the iceberg. Im just curious as this hole is huge now compared to what it was, and it acts like it needs to be bigger, so i figured id ask before i made it any bigger adn see how big some of you guys have had to make the hole