Xfi 2.0 question on lt1

[KRatcliff]

It sounds like you are using the IAC. Disconnect that sumbish. You don't need it and should solve your problem to allow the throttle body to simply close to your set idle point.

[Pierce Jones]

I was having similar issue last year with Holley HP and IAC controlling. I tried tuning decay etc. I couldn't get it to work well.

Thanks to posts on this site I finally unplugged the IAC this year. Much better returning to idle along with better idle quality.

[L.Fite]

So... I'm a carb guy, know zip about FI...
What exactly is the IAC supposed to be doing?
Is that similar to the Idle control that was to up the idle when the A/C was on, back in the carburetor days?
Or something else.

Always curious about how things work.

[KRatcliff]

Originally Posted by L.Fite

So... I'm a carb guy, know zip about FI...
What exactly is the IAC supposed to be doing?
Is that similar to the Idle control that was to up the idle when the A/C was on, back in the carburetor days?
Or something else.

Always curious about how things work.

That is it pretty much and why we can disconnect them.

[Kdw1403]

Will disconnecting the IAC hurt the performance performance of ET or MPH?

[pmrphil]

Originally Posted by Kdw1403

Will disconnecting the IAC hurt the performance performance of ET or MPH?

Nope.

[pmrphil]

Originally Posted by L.Fite

So... I'm a carb guy, know zip about FI...
What exactly is the IAC supposed to be doing?
Is that similar to the Idle control that was to up the idle when the A/C was on, back in the carburetor days?
Or something else.

Always curious about how things work.

Idle Air Control - it's a computer controlled (sometimes poorly) air leak into the intake that a race car doesn't normally need.

[L.Fite]

Originally Posted by pmrphil

Idle Air Control - it's a computer controlled (sometimes poorly) air leak into the intake that a race car doesn't normally need.

LOL... ok so that explains what it is...
But why did the engineers decide it was needed originally?

Still curious...

[Jeff Niceswanger]

Originally Posted by L.Fite

LOL... ok so that explains what it is...
But why did the engineers decide it was needed originally?

Still curious...

With an IAC, all idle rpms are consistent. You start your car up when its 0 degrees outside, the car instantly idles at 900 RPM (or whatever).It will stay at 900 all the way through the warmup process. No need to stomp on the carb linkage to keep the choke from reving 2000 RPM in your driveway as it warms up. When you turn on or off the AC, it still stays at 900. When you go from park to drive, 900. If the engineers decide they want 1000 rpm when the air conditioning is on and in gear, but 750 when its out of gear (or vise versa), they just readjust the idle rpms in the program and the car will do whatever they want. If your in a stick car and you have to lock up the breaks at a streetlight, the IAC will catch the situation and not the the car die. If your tugging on the steering wheel and the power steering pump is binding up the engine, the IAC will keep the RPMs exactly where they need to be. With a carb, you needed to set the idle up higher to catch a lot of these situations, no need now, set it as low as you want. I'm sure somehow it saves gas, as it all adds up
There was also something to do with the emissions. I cant remember all the details, but the engines needed to idle faster while getting the 02's up and heated ( they don't work when their cold) so the closed loop could handle the emissions issues. During that short "heating period" time the emissions went out of wack. So they "Idled up" for a few seconds on a startup/restart to keep the emissions down during that short period until they switched over to Closed Loop. Usually around 7 seconds

[L.Fite]

Got it...
Kinda what I suspected...
Is it tied physically to the throttle shaft or just lean/rich the mixture via controlled air leak?...

A friend resto-modded his street car with an LS-X and it hunts at idle...
Doesn't really seem to run like I would have expected a computer controlled car to run.
Seems rich all the time too...

Sorry for the questions but I really don't know anything about modern fuel injection.
Trying to learn.

If it ain't got pills or jets I'm lost!...