Idle Strategy.

[peter paul fenske]

At 10:42 AM 7/29/96 PDT, you wrote:
>
>
>Could anyone tell me a good way to handle startup to idle, I understand 
>there are a couple of ways.
>
>I believe I've seen a system where idle speed is set with a base throttle 
>opening, then modifies amount of fuel to hold idle.  Another with an idle 
>control over air as well.
>
>How should the fuel be mixed on startup?  Is cranking a matter of throwing 
>in heaps of fuel on startup?

Usually the Idle Air motor is set to open to a predetermined opening position
144 steps or so from closed in a gm system.
Then a certain pulsewidth is used to get a fairly rich start up mixture.
There is usually a table with pulsewidth(a/f ratio) to start up temp.
Also a clear choke function is used. Above 80% throttle opening during
startup the injectors are shut down. Injectors are usually assynchronous(not
always) since there can be a long time between injections at low starting
rpm. 

Transition to runmode can be handled in a number of ways. Use a table of
number of engine revs to temp. Or a set rpm can be obtained before switching
to run mode. 

Then idle control is used to obtain a predetermined rpm based on a temp lookup.

>
>Is engine speed an adequate feedback variable to hold idle by modulating 
>fuel?

Only when very hot. Usually closed loop after a certain operating temp or
a time period has passed.
>
>Is EGO even a consideration when starting/idling, or could cold temperature 
>render it useless?
>
Ego has to be quite hot. Even electrically heated ones take some time to work.

>How relevant is intake/block temperature to all of this?
>
>In short, what's a good way to handle idle?

Lookup table of idle speed to temp. Offsets for P/N, airconditioning, overtemp
ect. Also reset Iac every so often. And use a relatively slow control loop.
Even so oscillations happen.

>
>
>thanks,
>Matthew Lamari
>mlamari at origin.ea.com
>
GL: peter