How to silence the IAC in a 7747 GM TBI

First post on here - I've been lurking for a while now. Unfortunately, the admins have opted to not allow searches for three characters and my question doesn't seem to be too far out, so here goes. I've installed several GM TBI 7747 systems on my various Jeeps. All AMC V8's. They all run good and I've tuned them to get decent power/mpg's. I'm setup with a Moates autprom/winaldl/etc.

What are some good values (in tuner pro) to start messing with to silence the IAC? All of my rigs have that IAC 'hiss' when hit the throttle. More pronounced when cold, but always has that hiss. Sometimes I can hear it at idle.

Thanks and GREAT site! :rockon:

Blake, can't help with the IAC question, but here's a hint for searching forums such as Gearhead-EFI that don't allow 3-character lookups (I believe this is a search default): Use Google to search for your term along with a site specifier. It would look something like this in the Google search box:

iac site:gearhead-efi.com

The other cool thing is you can use all the Google tricks (such as double-quoted phrases, - on words you don't want in the search, etc.) to do your search.

Search sucks in vBulliten! I'm getting a better search plug in this winter...

Before you go turing off a good thing you can get rid of most that hiss. With an open element air filter or filter off you will here it. Shouldn't have an open air filter anyway...

Throttle blades need a min air adjustment when rebuilt or when old, the throttle blades close with age so IAC counts go up!
More airflow to mix fuel and air is good with injectors above throttle blades and less air going through IAC making it load!
So warm up engine and drive. Then check IAC count, 20 tops, if higher then go in 1/4 turn.
Turn off engine for... should be 5 seconds but wait 30 then restart so ECM finds TPS 0% and restart.
Rev engine after it goes closed loop to clear out wet intake. Check IAC counts. Rinse and Repeat.
When done check and adjust TPS voltage to .54 is considered perfect but close is fine... .65 ? I've been told it does not matter till 1.0 volt but ?

HTH!

:popcorn:

Well I've spent the last hour reading this; http://www.diy-efi.org/gmecm/papers/747iac.txt It talks about the operation of the IAC.

I made a couple of adjustments to some of the IAC settings in the BIN, but that didn't help much.

I'm gonna work on adjusting out the throttle plates and go from there.

This leads to another question; How can I adjust my TPS more than it wants too? I've already hollowed out the holes to the point where there's barely anything left.

That's a great paper on IAC, in the next version of $42.xdf I have all that stuff in the Paremeter Comments, and all the info from the Closed Loop Fueling stratagy paper.
http://www.gearhead-efi.com/Fuel-Inj...obert-Rauscher

Can't get enough hollowed out for .54 volts? If it's close don't worry... or bend the tang on back. :innocent2:

1st off, are we talking GM TB's? A "TBI 7747 system" could only refers to the control module that's used and doesn't actually say anything about related components.

How do you know the hiss is from the IAC? Throttle plates are a huge disturbance to airflow and can cause all sorts of noise. It's aggravated on engines with low end cams and high vacuum. Crossfire engines are known for throttle blade "hiss" at low and medium throttle openings. We've had several Dodge 318 / 360 powered vans in our fleet and the throttle whistle there is really noticeable. And BBK throttle bodies... I've heard some of those that really scream. As a test you can use a plug to cover the IAC opening with the throttle open and see if the noise disappears. If it is IAC noise, try working with the throttle follower. I'd open it as far and as fast as possible to get the valve out of the way then see if the vehicle is still driveable. You could disable it but you're actually limiting total airflow that way which goes against the hotrodder's credo.

If it's the throttle blades, well, we may have to take a crash course in aerodynamics to solve that one.

Good advice - thanks!

I have a junkyard TBI system on my current DD, which is a Jeep Grand Wagoneer with an AMC 401. It's a GM TBI from a 87-91 truck. Harness and all.

I played with the IAC throttle follower settings in Tuner Pro last night and that seemed to have a helped on my 5 mile commute to work.

It currently has a very small air cleaner on there which may be contributing to IAC/throttle plate noise... I"ll swap it out with a stock air cleaner and see if that helps...