i am not able to get my IAC's into range 60-70's at hot idle. if i get them into this range the car will not idle at all. i have an aggressive cam, procharger, etc. in my 2000 Z28. i hear that you always need to get the IAC's into this range before you do any tuning. how can i get them in this range if it will not idle by turning the set screw on the stock throttle body in?

 

I think as long as the idle motor is not at one end or the other you good. I forget what the max is, but as long as you are below that you should be good.

 

you need to get fueling correct before you can do idle
then when you get IAC in range, you will need to adjust Idle airflow tables.
also if you go past a certain point on the TB screw... it will no longer be able to reset to 0%.. so once you move it...do a TPS reset(unplug it, key on, key off, plug it back in, key on, key off, back to key on.)
once you reset it, if it doesnt read 0%(or 0.4 at the max) then you have gone too far...
I like to purposely turn it too far, reset it, see what the percentage is, and then back it down till it reads 0 in the scanner).
if you still cant get it far enough, you may need to slot the TPS sensor so you can twist it and move your set screw furter, or you may need to drill a hole in the TB.
I've noticed that our ls1 vehicles tend to respond better to a hole in the blade.. it keeps better off idle response because of the shape and rate of opening of the TB stays the same, which means the change in incoming air stays the same as well
you may also need some changes to your spark timing if it still wont idle.
everything has to work together.

as far as the "if its in range at both ends"
this is correct... with the exception that typically it wont be in range if you arent close to that 60~80 IAC counts
when its cold it needs a lot more air...the IAC can only move to 310, and typically if you arent near that 60~80 hot, it wont open far enough when cold..
this usually means cold starts will suffer, surge, or you will have to keep your fott in it to get it going when cold.

 

Don't get hung up on a number.

60-70 may make sense for stockish. But it represents
an idle airflow against an idle pressure drop. When you
add a cam and the parasitic load of a blower, you are
going to need more air mass (to make the idle load
power) and you're going to pull less of it per position
against your elevated MAP.

Your IAC air channel if it's stock geometry, will not
limit airflow until you get well over 200 counts. Don't
be afraid to go to 100 or whatever if that's what the
motor needs. Get it idling first, then get airflow to be
measuring accurately, then play with fuel, spark, air
until you've driven it to the lowest MAP at desired
idle RPM. That's as good as it gets, for the realities
of the mechanical setup.

Just like the old days with the vacuum gauge only
you need a thousand bucks worth of gizmos now.
Did you ever give a **** whether the idle bleed screws
were out 1 full turn instead of 3/4? Noper....

200+ IAC counts is a whole lot of air. I bet you don't
see that kind of demand once the mixture is right.
If you see over 250, ever, then think about whipping
out the drill.

 

Don't get hung up on a number.

60-70 may make sense for stockish. But it represents
an idle airflow against an idle pressure drop. When you
add a cam and the parasitic load of a blower, you are
going to need more air mass (to make the idle load
power) and you're going to pull less of it per position
against your elevated MAP.

Your IAC air channel if it's stock geometry, will not
limit airflow until you get well over 200 counts. Don't
be afraid to go to 100 or whatever if that's what the
motor needs. Get it idling first, then get airflow to be
measuring accurately, then play with fuel, spark, air
until you've driven it to the lowest MAP at desired
idle RPM. That's as good as it gets, for the realities
of the mechanical setup.

Just like the old days with the vacuum gauge only
you need a thousand bucks worth of gizmos now.
Did you ever give a **** whether the idle bleed screws
were out 1 full turn instead of 3/4? Noper....

200+ IAC counts is a whole lot of air. I bet you don't
see that kind of demand once the mixture is right.
If you see over 250, ever, then think about whipping
out the drill.