Haltech E6A - Manual (Page 75)

75
Chapter 14
Idle Speed Control
14.1 Description
A bipolar stepper motor may be used to control the ingress of additional air to the engine while
the throttle is closed. This is useful for maintaining steady idle under changing load conditions,
e.g. as air conditioner compressors or headlights are switched on and off. The stepper motor
may also be programmed to increase the idle rev-rate just after starting, or while the engine is
still cold.
14.2 Using the Idle Speed Motor
In order to use the idle air control function, you must have the following:
- a suitable idle speed stepper motor*;
- an idle air circuit bypassing the throttle plates;
- E6A programming software and cable.
*NB: use only a bipolar stepper motor with two separate windings (four wire), each with at
least 30 ohms resistance. Your Haltech
TM
representative can supply you with a suitable motor.
Use of three- wire stepper motors may damage the E6A ECU.
The idle air circuit draws filtered air into the engine around the throttle plate, as suggested in
figure 14-1. Normally this is done via an air bleed into the manifold. A valving arrangement is
used so that the idle speed motor pinches off the air into the engine. When the engine is below
the desired idle speed, the stepper motor's plunger retracts to allow more air to enter the
engine. When the idle speed is too high, the plunger extends. If your engine does not already
possess an idle air bypass circuit, a suitably machined aluminium block is available to mount
the idle speed motor. A balancing system or plenum arrangement should be used if employing
individual throttle bodies, so that all cylinders benefit equally from the additional air.
NOTE: You must ensure that the manifold's air bypass aperture is sufficiently small so as to
not over-rev the engine when stepper motor is fully retracted. Fitting a large idle air valve to a
small capacity engine can lead to poor idle control and dangerously high engine rpm with no
throttle control.
Fig 14.1. The idle-air circuit.
There should be sufficient airflow around the
closed throttle plates to permit the engine to
idle slowly even with no air passing through
the idle bypass circuit. The throttle stop
should be adjusted to ensure this is the case.
Remember that the throttle position sensor
will need re-calibration if the throttle limits
are altered.