High idle after start

[mrvette]

Ludis Langens wrote:
> 
> "Bruce Plecan" <nacelp at bright.net> wrote:
> > - -----Original Message-----
> > From: Scot Sealander <Sealand at clarityconnect.com>
> >
> > <snip>
> >
> > >> When I initally start the thing the rpm goes to over 1500 for 15 to 20 >
> > seconds then settles back to idle...
> > >
> > >You indirectly messed with the open loop settings for the IAC.
> >
> > Mind shedding a little more light on this?.
> 
> 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
> way...


I don't know about other GM #'s   but I was told that on the '87 vette, the one
that uses the MAF sensor, and for sure 1227730 MAP hookup,  by the guys that did
my hot rod chip....that the computers do definately look for specific idle
speed....~700 rpm's in each case....there are several IAC motor pintle shapes, 
not sure as to why they bother, but they have a definate affect on idle speeds
under various conditions...
airflow charactoristics are changed under differant conditions..GENE
> 
> 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.
> 
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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