Throttle body hole vs idle airflow

[99LS1SS]

I'm tuning a 2000 TA with heads, cam, intake and throttle body.

If someone has drilled the hole in the throttle body too big would that cause the desired idle airflow to be lower than a stock vehicle?

I've adjusted the throttle blade completely closed and the idle is still higher than I want it to be, when the engine is warmed up. That's with all of the adaptive spark and airflow turned off.

Does this theory make sense?

Thanks.

[Britt2020]

I'm no tuner and this may not even be possible, but couldn’t you make up the difference by adjusting the IAC a bit?

[DSteck]

If the IAC drops to zero and the throttle is completely shut, and it still idles high, then I'd say the hole is too big.

[99LS1SS]

*Edit since I misread your comment.

It has dropped to 0 and it hovers around 30-40 when warmed up.

[Alvin]

When you drill the throttle body the effective area vs IAC steps table changes. When you fix that table your actual idle airflow will start matching up with desired and also "real" airflow. I've never seen it make much of a difference unless you have an enormous cam huge stroker setup that might get close to the 39gram/second limit.

never seen it make a difference but we fix them anyway just in good clean tune practice.

[vette_c6]

damin guys ! i have seen 1000 RWHP cars !
never drilled a hole !

Good Luck !

[99LS1SS]

damin guys ! i have seen 1000 RWHP cars !
never drilled a hole !

Good Luck !

I know. I wish they wouldn't have drilled this one.

[99LS1SS]

When you drill the throttle body the effective area vs IAC steps table changes. When you fix that table your actual idle airflow will start matching up with desired and also "real" airflow. I've never seen it make much of a difference unless you have an enormous cam huge stroker setup that might get close to the 39gram/second limit.

never seen it make a difference but we fix them anyway just in good clean tune practice.

In this scenario, it went from a stock throttle body to a fast 90mm throttle body. That that cause me to increase or decrease the Desired IAC Steps vs. Desired Idle Effective Area table? And by how much?

It's got a 232/234 598/599 113 cam.

[edcmat-l1]

I know. I wish they wouldn't have drilled this one.

They come from the factory with a hole in the blade.

[99LS1SS]

Any idea of what the stock hole diameter is?

[Alvin]

roughly 3/16

A good job with a hole I think turns out better than adjusting the throttle stop.

[2xLS1]

They come from the factory with a hole in the blade.

You would think those dumb ass GM engineers would know better. The must not read the interweb forums much.

[Ben Charles]

Sometimes a hole is neccessary, on the LT1's you can slot the TPS, on the LS1's you really can't, I couldn't get the IAC counts down on tune I did and with a quick "wack" of the throttle the engine would actually die, took the factory hole and ended up going to sizes larger than factory, worked like a champ.

[vette_c6]

Sometimes a hole is neccessary, on the LT1's you can slot the TPS, on the LS1's you really can't, I couldn't get the IAC counts down on tune I did and with a quick "wack" of the throttle the engine would actually die, took the factory hole and ended up going to sizes larger than factory, worked like a champ.

in LT1 you can increase Timing to something like more then 28 degrees
even you can go to 30
but we are talking about LSx

my point is ,, fix the tune better then start drilling ,,,

u might be right on the LSX series ,, but i wont Do it
few days ago i have Tuned a car with a help of some friend from the tuning school
i have learned alot ,,
the car was Stock engine ,,
heads cam Meth P1SC 12 pounds of booost
2.5 bar MAP sensor ,,
and guess what ,,, idle was like a car from the factory ,,,

my point is ,, everything can get fix from the Tune ,,
if you Couldnt take it to a proffesional Tuner ,, and see if he desided to Drilled a hole ,,,


sorry for saying that guys ,,, but thats a FACT ,, not everything you get it throuh the internet have to be write ,,,
if you guys are right about the drilling hole ,, ,then i guess
guys who are tuning 1000 RWHP they are GODs

enjoy your day ,, at the end you might get it right ,,,, but it doesnt means it the right way

[edcmat-l1]

^^^What don't you understand about "they come from the factory with a hole in the blade"? The early LS Fbodies came from the factory, with a hole in the blade. Has nothing to do with power output. It is an IAC idle airflow issue.

[vette_c6]

you are right

[LSxpwrdZ]

A big healthy camshaft, 102mm throttle body with a smaller passage for airflow to the IACV, and a FAST102 or the like aren't factory. So with that said sometimes its impossible to keep idle steady by ONLY adjusting the tune. With the blade shut on my cam only Formula with no hole in the blade the IACV will not supply enough airflow to idle. I temporarily cracked the blade open some to get IAC counts down but I will be measuring the stock hole in a stock throttle body and drilling mine.

Electronic throttle cars might as well be omitted here as well cause they are a dream to idle tune compared to a slow junk IACV!

I always like to keep the blade shut as far as it will go before it sticks so that it is more consistent at shutting off airflow to the manifold. I've experienced shaft play in some cheaper TB's that when cracked open a hair they move around when the throttle is closed to the bump stop and allows different amounts of airflow in each time the blade is shut, this will keep you chasing your tail with idle tuning! The only way around it is to allow airflow by the blade somehow. My PCV is blocked off also which is a significant source for idle airflow (many people forget about that). In the end a setup that requires much more airflow at idle is going to have to get it somewhere cause the IAC only has so much control.

[mowton]

From my understanding on a drive by cable setup, without the hole, you would have to adjust the blade open to the point you would exceed the .7 v max on the TPS and max out the IAC stepper counts which the PCM uses to determine it is in idle or not and maintain adaptive idle control.

On ETC setups (drive by wire), the you can adjust (through the tune) the TPS % for idle and the PCM controls the throttle blade instead of the IAC motor as they don't have one. On rare occasions, I have seen where tuners have had to drill a hole in a DBW setup, but not personally.

Ed M

[Ben Charles]

in LT1 you can increase Timing to something like more then 28 degrees
even you can go to 30
but we are talking about LSx

My car is an LT1, but the car I was tuning was am early LS1 with a stock 75mm TB with a FACTORY HOLE

[gn2beatu]

If you end up determining the hole is too big (for your combo), you can always fill the hole with a rivet as a quick fix/test, then if it fixes it, you could remove the rivit, and tig weld it shut and grind smooth.