ShawnZR-1

What should the IAC counts be at idle? I'm showing around 12, is that too high or low?

Thanks!

Aurora40

That sounds pretty good to me. You want enough so that the ECM is in control. 5 or more is probably pretty acceptable. Is that with the car fully warmed up?

Dominic Sorresso

Shawn,

Twelve is fine. I've always tried for less, say 5-8. You can crack open the TB a bit to bring the IAC counts down. The bigger the TB, the more you want air to go thru the throttle blades and not bypass via the IAC opening. Keeps up the air velocity.

Aurora40

Why would the air have any more or less velocity once in the plenum? Also, is velocity relevant at idle?

tpepmeie

Maintaining good velocity through the throttle bores is really only a priority for TBI systems, where the fuel is added at the TB. It helps prevent puddling and helps atomization.

The benefit of low IAC counts for a port injected engine is more about how responsive the engine is to transients and coming back to idle. I also tune for high single digit IAC counts at idle, which takes most of the air control away from the IAC program. With the motor able to hold a good idle on its own without relying on the bypass air, then I can get more aggressive with things like the throttle follower action and decay rates. The result is an engine that has a quick response to throttle tip, and a very fast recovery to idle speed.

Todd

terryszr1

i have a? on both my 90s my Iac when cold is around 29 when they are fully warm they are 0. both cars run really good but am IO missing a problem

tpepmeie

Possibly a vacuum leak preventing the engine from reaching the warm idle speed. The IAC is fully closed (zero steps), but the idle speed is still above the calibrated value. What is your observed warm idle rpm?

Also possible, but less likely, is that the throttle blades could be misadjusted, allowing too much air to enter when closed.

Todd

FASTAZU

My 91 shows 20 stock chip 675rpms and 30 with SGC chip 900rpms

ShawnZR-1

Wow, great information guys! Thanks!

Steve, I don't know if I've ever seen counts that high, of course, I've only scanned one other ZR-1! I'm by no means an expert here!

One question: Why don't I see an IAC follower table in TunerPro RT? Does it exist for a '91?

FASTAZU

I have never checked any others.. My idle is rock solid no vac. leaks.

terryszr1

the black car tuned by corey has an idle speed that suppose to be 800 but runs 875 to 900 . red car z industries ship 675 and runs 850 .. so would i look for a vaccume leak first i have tried the propane method on both cars and havent found a leak. how does one set the throttle blades ? thankyou for any help.

Dominic Sorresso

Its there in the cal. Nobody has created the item in the .xdf. There are quite a few items that are in the cal but aren't found in either the TC or TP tdf/xdf. With a hack of the code, these could be easily added.

Todd,

My TBI's were 2.13". I didn't need extra flow coming from the IACs.
I minimized IAC steps to:

1. Maintain a smoother idle even while using a cam with a 108d LSA. The Xfire motor uses "diffusers" below the TB to maintain swirl keeping fuel in suspension.
2. At part and full throttle, throttle response was significantly improved in much the same way as a "dry manifold" design.

I agree that a goal of tuning is to have the ECM "intervene" as little as possible. The better the "mechanical" tune of the motor, the better the overall tune is. The CW that "the ECM will take care of it" is bogus.

ShawnZR-1

...sooo, who wants to hack the code? :

Dominic Sorresso

phrogs

waht are you using to read the IAC?

ShawnZR-1

DIACOM.

ShawnZR-1

Hmmm, so nobody wants to delve deeper into the code eh?

Well, I guess I can go without sleep for the next few weeks then... Time to dust off the binary side of the brain.

FASTAZU

Sounds like its all you..

ShawnZR-1

What are you talking about, all me? Get your butt up here and help me!

4DSZR1

Did you try posting your question here?

http://www.zr1netregistry.com/forum/index.php