IAC steps

[tumleweed]

Is the proper IAC count to be achieved idling in gear or park? sorry

[dave w]

The attached .pdf should have helpful information on Tuning the TBI, including the IAC.

dave w

[steveo]

for your LT1? the important thing is that most of your idle air comes through the idle passages and not the throttle plates, so the LT1 should have its throttle plates pretty much completely closed.

there's no 'proper iac count' for an lt1, just an operating range. if there was, and yours didn't match, how would you achieve it? by tuning? raising and lowering idle speed itself? opening/closing the throttle plates?

i'd be worried if it's lower than 20 or higher than 100 in any condition.

if the IAC counts are too low, something is broken. if they're too high you probably need to enlarge the bypass hole in the throttle body to get more idle air.

you need the IAC to remain open a reasonable amount in all idling conditions, both park and neutral. above 0, it's open.

[tumleweed]

I can't get them any higher than 49 with the throttle plates all the way closed ( throttle lever not touching the stop screw) but I think I drilled the bypass hole. what is the original size of the bypass hole?

[steveo]

what's the lowest IAC count you've observed?

[tumleweed]

I can open the blades and get as low as 35-37 any further open and they start to go up

[steveo]

if you open the throttle plates the IAC counts should go down, not up.

i don't see a problem, why are you even playing with it, your IAC counts sound fine ?

iac counts aren't some tuning variable you need to nail like BLM or AFR or spark advance. you just need to make sure you don't run out of 'travel' so the IAC stops being able to control idle.

do you have a poor idle?

[Fast355]

In my experience 30-50 IAC counts will help fix the split BLM value at idle on a LT1. At Zero counts that split can get fairly wide.

On the otherhand a TBI likes low IAC counts. 5-10 steps on those as it helps pull fuel past the throttle plates to have more air flowing past.

[steveo]

In my experience 30-50 IAC counts will help fix the split BLM value at idle on a LT1. At Zero counts that split can get fairly wide.

no, in your experience (and everyone elses), sufficient airflow through the idle passages helps "fix the split BLM value at idle on a LT1"

idle air is the sum of the idle bypass hole plus the IAC counts. this guy has maybe drilled it. your numbers don't really relate to him anymore. the IAC count number doesn't mean anything without a reference point. maybe on a bone stock engine but that's not what we're tuning

if you drill it out big enough, zero counts would still have sufficient flow through the idle passages, but the ECM wouldn't be able to affect idle speed properly

[tumleweed]

NO, it idles ok.
I'm a tinkerer and I read this here and that over there and I still end up asking a stupid question, this is way over my head.
prob will go back stock and not worry with all this.

thanks Mike