Xfi 2.0 question on lt1
 

When I rap the throttle and the rpm goes up. It seems to take a long time for the rpm to get back to idle. When it does idle down It idles at 1200-1300 rpm. What can I do to make it go back to idle quicker?

Re: Xfi 2.0 question on lt1
 

Adjust the throttle followers

Re: Xfi 2.0 question on lt1
 

Like previously stated, if the car has an IAC ( Idle Air Control) on it you can adjust the throttle follower and try to help it. But an active IAC on a Superstock car is rare. I doubt you have one. Most of them are unplugged, blocked off, gutted or deactivated in the program. Its probably just a ill tuned map with the tune needing much more air than it should to idle, so the throttle body blades are opened way up, which in turn causes a sloppy return....
Make sure you don't have any type of vacuum leaks, especially at the map sensor or hose. Vacuum leaks play havoc with FI tunes...
You didn't mention whether is does this right after its been started, of after its warmed up and siting there running. If its right after a restart it is the After Start Enrichment and Decay rate,. Probably more so the Decay rate.

Re: Xfi 2.0 question on lt1
 

Anybody got a screenshot of a properly adjusted throttle follower? What is the proper way to adjust the throttle follower? Which way does what? Sorry to be so stupid.

Re: Xfi 2.0 question on lt1
 

It does it most all the time. Cold or warm. It’s a B-C/SA.

Re: Xfi 2.0 question on lt1
 

What is decay rate and what’s the proper way to adjust it.

Re: Xfi 2.0 question on lt1
 

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.

Re: Xfi 2.0 question on lt1
 

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.

Re: Xfi 2.0 question on lt1
 

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.

Re: Xfi 2.0 question on lt1
 

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

Re: Xfi 2.0 question on lt1
 

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

Re: Xfi 2.0 question on lt1
 

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

Still curious...

Re: Xfi 2.0 question on lt1
 

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

Re: Xfi 2.0 question on lt1
 

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!...

Re: Xfi 2.0 question on lt1
 

Its hunting because its not adjusted right, but big cammed cars and IAC are a challenge. The IAC has to be timed and adjusted to match up with the basic fuel map. The IAC is a little stepper moto or servo. It has a pindle, basically a big needle like in a needle and seat of a carb. It screws itself backward and forward seating, unseating, screwing just a little bit out, or a lot out. The farther it backs out, the more air it allows to "Go Around" the throttle body plates which in turn increases or decreases rpms. Thays about it, their isn't much to them

Re: Xfi 2.0 question on lt1
 

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

Re: Xfi 2.0 question on lt1
 

Nope.

Re: Xfi 2.0 question on lt1
 

Thanks
Makes sense.

Can I PM you some day with more questions?
(rather than stepping on this thread)

Re: Xfi 2.0 question on lt1
 

Sure, anytime

Re: Xfi 2.0 question on lt1
 

Start a new thread. I'm learning. I've had an 87 5.0 Mustang since new. I still know carbs better. lol

Re: Xfi 2.0 question on lt1
 

I've never been called the brightest bulb in the box so being a newbie to actually running a computer car, I took an EFI class. In the class we talked about the IAC. How many racers back in the day had controlled vacuum leaks on their cars in an effort to get more air into the motor? The IAC is a CONTROLLABLE vacuum leak and you can fuel around with it. Another thing I learned was do NOT unplug the IAC while the power is on. It will blow the circuit board in the computer and yes, Fast is aware of this glitch. I know, it happened to my motor while it was on the dyno and I wasn't anywhere near it. It is amazing what we can do with these computers compared to an OEM unit.