High idle after start

[Bruce Plecan]

-----Original Message-----
From: Gregory A. Parmer <gparmer at acesag.auburn.edu>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Friday, October 09, 1998 12:34 PM
Subject: Re: High idle after start


There is an ol saying about one than one way to skin something.  If you
only look in one place for answers the only answers you see are what's
there.  Now, I not looking to ruff feathers, but, there are other items to
consider other than the high idle at restart.  You can lower the cold
idle commands down.  There are a few values along the 400rpm/70+
MAP values, and 400 rpm PE enables, that also can play a part in all
of this.  So saying 25 IACs is best is for only what your addressing....

On the Cross Fires, you can extend the IAC's, and then just run on one
just fine.  The plenum is large enough to handle that.  Just be sure, you
have the balance right.

Personnally the 1,500-1,800 cold starts are way too high for me.

The pintle shapes while having some effect at idle have more to do with
sudden throttle movements, and passing situations, where it jumps lots
of steps quickly.  IMHO.

>
snip
>> > It has to do with how fast idle on a cold engine is implemented.  In
the
>> > 1227170 ECM, and probably others, the IAC is simply opened another _x_
>> > counts from the learned warm idle position.  The ECM does not try for a
>> > specific fast idle rpm.  (Surprise!)  I think the '7747 is the same
>>
>> > If the learned idle IAC position is too low, then the increase for fast
>> > idle is a much bigger percent change than it was meant to be.
>> > Similarly, if the learned position is too high, the increase won't be
>> > enough.  This is why the IAC position for idle is important.
>
>How timely!  I fired up my '7747 controlled hodge-podge of
>parts last night.  The manifold is a Cross Fire Injection
>unit with 2 IACs--twice as fast on high idle after start.
>One of 'em may get unplugged until I get a chance to program
>that out.
>
>As I understand it, the IAC expects to be running in a
>certain range of steps. If the throttle is too closed
>then too many steps of IAC are required and if it's too
>open then IAC may close completely trying to maintain
>the pre-set idle RPM. True?

If you read the above, noone has mentioned anti-stall.

The IAC is tied to several things.
>
>There must be a tune-up manual somewhere that describes
>this, but I ain't got it. Can someone describe what
>values we should be shooting for on IAC...like what
>would be normal for the '91 PU. I'll document as
>I go.   Lord knows progress is slow enough.
>
>For starters...tranny in N and warm engine,
>1) key on, engine off       (prep for start) = ??

Often 150

>2) key on, engine idling         (warm idle) = ??

Book 10-30, my Preference 0.

>3) key on, engine off idle         (dashpot) = ??

Hot restarts can be about anywhere, 30-50 most common.
>
>Discussion has been of "2)".
>So far the consensus has been that an IAC cnt of 25 is
>normal for idle and that Jason's "9" is too low
>and that's the cause of the high idle. Guess what
>fellers...mine's "71" and exhibits EXACTLY the
>same behavior.  SNAFU may be a bit too critical, but
>it does appear normal...as if GENE needs encouragement. :)
>
>My values are abnormally high because I set idle to 1000
>RPM for initial tuning. Nevertheless, I've got
>1)=~145, 2)=71, 3)=~91
>Telling me that my throttle blades need to be opened a bit
>and that my preset idle RPM needs to be dropped. No?

How happy is the AFR, BL/Integ is ?????....
Bruce
>
>-greg
>
>
>