system is a stable and fairly accurate open-loop calibration. Without this the control strategy CAN NOT WORK effectively or even at all.
Note: Closed-loop refers to ANY type of control strategy with feedback. Idle means the speed at which the engine sits during its rest
state. Closed-loop idle means controlling that speed using a control strategy with feedback. http://en.wikipedia.org/wiki/Closed_loop
Steps
Perform all of the below without headlights, aircon, large stereos, etc active. Such devices can be used to evaluate the PID setup afterward.
- Give your engine just enough air-flow to survive a cold start at slightly too low an RPM and hold at slightly too high of an RPM once warm
- Tune your engine temperature enrichment curve(s) to facilitate acceptable running during the cold start period
- Close off the fixed airflow such that the idle valve will do all of the work, especially important with big Bosch valves
- Setup open-loop idle control, and set a curve of duty/steps vs. engine temperature that provides a pleasant RPM at all temperatures (eg 1500 cold, 800 warm)
- Setup a target RPM vs. engine temperature curve that matches your unloaded reality as provided by the open-loop curve
- ONLY now should you engage closed-loop PID engine speed control and tune the PID parameters in the normal fashion
- This applies to 2 and 3 wire PWM, and 4 wire stepper systems equally.
- Engine temperature is a reference and can be based off of coolant temperature or head temperature (if air cooled)
- There will be other logic and settings to ensure good behaviour when rising into control and falling back down into control.
- PID can be read about here: http://en.wikipedia.org/wiki/PID_controller
- PWM can be read about here: http://en.wikipedia.org/wiki/Pulse-width_modulation
- Steppers can be read about here: http://en.wikipedia.org/wiki/Stepper_motor
Fred.