Guys, it seems the right way to fix or atleast help the idle along in a cam car is to drill the throttle body to get your IAC counts in the 60-40 range correct (i'd rather not mess with the set screw)? Is this the first step to helping a car's idle get in line? Obviously items following this will include timing adjustments to the idle and high/low timing tables as well. Once the IAC counts are inline is it typical for most of you to still full with the Idle Air flow tables? It just seems without doing something to the throttle body that all of these change this table change that table doesn't seem to produce any posative change without being counterbalanced by a negative one (i.e. you get the idle stable during transitions but now you have a cruise control effect, etc.). Thanks.

 

I recomend adjusting the set screw some while keeping TPS in range. Because when you start getting your tune lined out you may have to close it up some. And if you just drill it you have to figure out a way to close the hole and drill a smaller one.

I adjusted my set screw till TPS read .59 volts, even enlarged the holes to adjust the TPS sensor to keep it under .59v, then I drilled the TB hole little by little till I was in the 40-60 range. As I moved along with the tune I started having a surging issue, found my IAC counts in the 30's, closed the blade up to bring them back in line.

 

I think what's important, is that the IAC counts never
bump up against the stops at any condition across the
environmental envelope. And if you look at the IAC
area vs counts table you can see that some of the
counts range is "dead" - no area change for IAC
counts from 0 to 12 (dead closed), and from 114-128
(open is open).

But hot idle is only one side of the story and not
likely the more challenging bit; there the air demand
should be near its minimum. And if you are at high
counts at hot idle, cold is going to want plenty more,
maybe not get it. If you see cold idle IAC counts
are up in the 100s then you probably will have a
control problem where the car runs it up to the end
of range trying to get air, enters the "so what?"
area, this is where the lag comes in and makes the
loop unstable. Just like you want a sound system
that has way more watts than your ears can stand,
so as to allow the peaks to play clean, you need
some room for the control loop to overshoot in IAC
counts and not get bound up, or it'll get jerky.
You don't probably want to be at IAC=60 if that
makes cold start idle need to be 112. You want
to determine your min and max points and make
sure they both have room to move, and overshoot
the goal, without getting into the "dead zones"
at the end of range.

 

Instead of drilling the existing hole, I would recommend drilling a teeny tiny one on the other side of the blade (opposite of the one already there) and going from there. That should eliminate the problem of drilling it out too much...after all, math tells us that:

Area of a circle = pi * the radius^2

Increase the radius (with a bigger drill bit), and you increase the area a lot

 

I have never been a fan of drilling a hole in the TB until recently. We have always used programming to get around drilling a hole but it seems like it helps on a couple of cars. We have had a few cars that have had erratic idle and TPS showed 18-20% to idle. After drilling a small hole the TPS reduced to 11-13% but the idle was slightly more stable.
Phil

 

Thanks for all the input. I'll be implementing this tomorow on a 02 ss with a magic stick and will report how it goes!

 

For me it wasn't an issue of drilling the hole too big. What got me is as I progressed with my tune the engine required less and less air at idle. I'm sure this is because I went from stock 02 cam and tune to a cam that specs at ~242/249 on a 110lsa.

But you are correct the smaller the hole, the lesser the change in area, and the better chance you have of getting it as close as possible.

 

I'd personally open the stock hole up to 13/64"

and then:

Idle Limiters --> Idle Speed: 950

Idle Limiters --> IAC Park Position: Raise all points from 40C and up to 21

Idle Limiters --> Idle Air In Gear: All points 60C and up to 8.6

Fuel --> Main VE Table: Multiply column 400 rpm by 60. Multiply column 800 by 80. Multiply column 1200 by 90.

Ignition --> High Octane Table: Add 2 deg to all points 400 to 1000 RPM, .08 to .32 g/sec


from there, my car always wanted less fuel at idle... so your may need to remove more fuel from the 400, 800, and 1200 rpm rows in the Main VE Table. I believe by the time I was done with my 231/237 cam, I had taken another 30% of fuel out of the tables after doing the 60/80/90 adjustment. However, you may also need to bump up the values some more in the Desired Airflow table.

If you get the dreaded cruise control effect, it can be counteracted by reducing the values in the Throttle Cracker and Throttle Follower Delay tables.

 

Base idle timing is also a good spark map to look at.
With a cam more timing will increase vacuum normally.

 

Drilled the throttle body yesterday and got the IAC Counts down to 68ish and the car idles very well now! Also smoothed the timing out at all tables close to idle conditions which seemed to help stabalize even further.

Quick question though, have you guys ever seen a CO240 Code (Traction Control System Code)? I went to remove the code with ls1 edit and it wasn't even included in editable codes? The guy who did the cam install claims this problem with the traction control (sometimes you can't turn it on or off while idleing, it just comes on and stays on or stays off and won't come on all when hitting the button) showed up after the cam install.

 

Are you throwing a p0121 or p0106? Those codes will cause TCS troubles. Check out this link if you do.https://ls1tech.com/forums/pcm-diagnostics-tuning/485439-codes-caused-new-cam-affecting-tune.html

 

106 actually. I just turned the code off for the time being and the light went a way and stayed away for the five minutes I spent with the car after doing so. I'm going to check out that link now. Thanks

edit: sounds to me like the right thing to do is raise the failure value to above the cam idle map pressure. will have to go back and look at that.

 

Let's not confuse things here. I always understood idle timing to be in the base timing tables alone. The high/low octane tables are for when you're on the gas. Yes, they need to be close so that when you transition between idle and non-idle things go smoothly. But, idle timing does not come from high/low octane.

 

Yep, that's my understanding as well. The low regions of the high/low tables are only used once the throttle is opened up enough to be considered non-idle conditions and the idle tables used below that TPS %.

 

ok..so heres my take on all of this....

*cracks knuckles*stretches hands*

so basically we all need to make our cams idle....
in an older setup with a carburator we had Idle bleeders....add more air to stabilize idle...
seems simple enough...
no computer to jack with...just get the fuel mixture correct and get the air for idle correct..easy enough


ok...
todays vehicles..and specifically the ls1 cars that this board was made for...
we have a computer that does hundreds of things at idle....and looks at so many thing to keep a stable idle..
first thing to address is spark timing...anything remotly close is good enough for most cams...for me 28*ish seems to work well..and you want it to be basically teh same in all the surrounding cells that your car idles in...
next thing to addres is A/F mixture at idle...get it in the stoich to slightly leaner than stoich values to begin with....


these 2 things alone are the biggest part of the idle battle...

now on to TB holes...
there are many things in the pcm that reference the TPS voltage and position...(or so I have been explained by people who have to wriet software to tune for a living)
some of them are looking for the default voltage that your stock TB has...
and some things dont care about the voltage and just want it to be 0%tps for idle.
in any case I prefer drilling...
you just cant go making huge adjustments and huge holes...
its much better to have several smaller holes as the area of a circle gets exponentially bigger with the bigger hole that you drill (see equation in post above here somewhere..LOL..simple geometry..you should have learned it in high shcool)
I think of the hole just like the idle bleeder on an a carbed car...cause that is what you are doing by driling...
the TB screw was designed as a bump stop to keep the TB blade from sticking when it goes all the way closed..just really keeps it from closing too far as they are usually machined to fit perfect in there so it doesnt leak extra air in there that it doesnt need

ETC vehicles dont have the same references that cable drive cars have..so they can get awy with a TPS position change..but it still has to be within certain limits
with ETC vehicles you can get to about 7% at hot idle with fans and ac off before it starts to screw with other stuff...

in general our IAC is supposed to take care of the differing amounts of air needed at cold idle vs hot idle...and they are very different amounts...on ETC vehicle it cracks the TB blade

the idea is to keep the IAC within it physical limits...but certan other things happen as well that can make it screwy when its way open...again the area of a circle is a lot larger when teh hole is bigger..so the further up in counts it goes..you get more and more difference betwen each step..
so if its up in the upper range too far then 1 step is too far and can lead to unstable idle...example being that it needs .1g of air and 1 step - .3g of air...then its too much so it goes back down and back up ...and as it overshoots it needs more and less and soon you have a swinging idle and as it gets too far it dies..LOL
so drilling helps keep the IAC in the lower range and allows the amounts of air that changes when the steps increase or decrease to be smaller amounts of change..allowing for more stability....
stock teh IAC is usually around 30-60ish with fans off and ac off at hot idle...
so we shoot to get it back to that range again with our cams..
obviously the cams require much more air..so we drill a hole to get there..
I even used a little math to get the are of a circle to get me close on the hole size needed...
I look at the steps it is at....vs steps I want it to be...
I look at the effective are table to get the size that it equates to


below is a pic of the table in HPTuners...
as an example well say I have 170ish counts wam and I want to be around 50-60 ish

I look at my table and see that 170 counts = 64mm^2and that 60counts is roughly 25mm^2 so I need to move it 39mm^2 from where its at...
using my math posted in the code there an 1/8th gets me almost 32 and 9/64th's is 40ish...
so I'm probably gonna pic the 9/64th and go for it.....
so far my math hasnt been wrong..and I have never had a problem with the hole being too big....
it is just simple math and the IAC values have been calibrated by GM (not that I always trust GM..but they seem to be right on this one)
teh IAC steps represent the IAC pintle hole...

and with the added aior and my IAC counts down to a more reasonable value then I have room to move on frigid cold days...
all of the stuff combined above will lead to a very stable idle with very little effort..
the only other important thing is to make sure the cam isnt choking on its own exhaust....

and I get Idle AFR correct before I drill the hole as AFR has a huge part of stable idle

and FWIW...I made a trex cam last week..idle at 800 rpm with no issues
and about a mont ago a 259/263 cam that idled at 850 with no issues

 

oh yeah..pardon any typos...my hands are dyslexic sometimes...my brain is not..LOL

 

Excellent information soundengineer, thanks!!!