High idle after start

[Ludis Langens]

"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...

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/