Holley COMMANDER 950 - Manual (Page 66)

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Figure 51 Idle Air Control
Desired Idle – The engine idle speed will be controlled by the ECU and can be changed at different temperatures. If the
engine is cold, the idle speed will need to be higher than if the engine is warm. This is because the oil will be thick and the
friction internal to the engine will be greater.
IAC Parked position – After the ECU is told to shut off, it will command the IAC motor to this location. By having the IAC
motor parked in a known location, it will enable easier starting and a better initial idle on the restart.
Minimum IAC Position – This table allows the user to cause the IAC to “follow” the throttle position. As the throttle is
opened, you want the IAC to open also. This is to keep the engine from stalling when the throttle is instantly released. The
IAC will not close lower than the throttle follower position, so you will want to set the throttle follower at zero for the idle TPS
position and quickly ramp the IAC open after that.
O
2
All parameters dealing with closed loop operation and the use of the oxygen sensor are found in this screen.
Figure 52 Closed Loop Parameters
O
2
Compensation Step Size – This table specifies how much fuel the ECU will take out or add to the current volume on each
step in an attempt to bring the air/fuel ratio to ideal. The base settings that ramp from 1 to 3 as the rpm increases are usually
ideal.
Seconds between O
2
Compensation Step changes – This table sets the amount of time the processor waits before further
adjusting the fueling amount. This is commonly referred to as the transport delay. After a fuel change is made, the new
amount must travel to the cylinder on the intake stroke, be compressed, ignited by the spark, push the piston down, leave
through the exhaust valve, travel down the exhaust tube, and be sensed by the O
2
sensor. If the values in this table are too
small, the ECU will not be allowing the new fueling changes enough time to be sensed by the O
2
sensor and would then be
making changes based on old information, not new information. If the values are too big, the ECU will take too long to settle
on a change. These values are based on the position of the O
2
sensor in the exhaust. The base map values are close for
sensors mounted in the collector. Sensors mounted closer can have the values reduced. See what works best for your
application.
Cold Start Delay – The amount of time the system will wait before entering closed loop operation when the engine is cold.
This should be about 180 seconds. It also must meet all the other closed loop parameters before entering closed loop.