High idle after start

[Ludis Langens]

mrvette <mrvette at bellsouth.net> wrote:
> > 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.
>
> 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

I guess I wasn't quite clear.  The ECM does look for a specific warm
idle rpm, ~700 rpm in your case.  It remembers the IAC position that
produces this rpm.  On the next engine start, to obtain a high idle with
the cold engine, the IAC is opened some preprogrammed number of steps
beyond the remembered position.  Hence, the fast (cold) idle rpm is not
controlled to a specific rpm.  This is why one car has an initial idle
of 1000 rpm, while the next one jumps to 1100 rpm.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/