Idle control valve

[Paul Beam]

>I have a question concerning the idle system used in EFI. How fast and what
>factors are involved in the closing of the idle control valve once the 
>throttle plates have opened ?

I worked a little on this at Saturn, before they were actually selling cars.
GM uses a stepper motor like valve, while some others, including Ford, use a
solenoid type system they control with PWM.

If I understand your question, I left the valve alone once the engine was no
longer under idle conditions.  I seem to recall that you want to control the
speed of the engine while the vehicle is below a certain speed, but the car
is moving you just leave it alone.  The powertrain people there told me that
was how it was done.

My system would actually help someone start in a manual transmission car by
allowing more air (and hence fuel) into the engine as they would start to
move.  Under deceleration, you can let the engine "race" until the vehicle
gets down to 15 mph or so.  You should be able to simulate this on a manual
transmission car by pushing in the clutch while rolling down the highway and
see what happens.

The only other issues are how fast can you make changes and how big.  The
answers are not often and not very much.  A couple of times a second is the
most you can get away with.  If you add too much air, you will kill the
thing unless you "cheat" and richen the mixture with an extra shot of
combustibles.

Again, this is how I did it on a hybrid GM system.  I'm not sure what others
have done.

Paul

R Paul Beam
Computer Systems Engineer
Johnson Bible College
7900 Johnson Drive
Knoxville, TN 37998
(423) 573-4517
(423) 579-2337 fax