Idle Speed Control

Idle speed is controlled by the SMEC through the Automatic Idle Speed (AIS) motor. The AIS is mounted on the throttle body assembly. The SMEC uses sensor input to determine optimum engine idle speed for any idle condition.

The AIS receives control signals from the SMEC to adjust the amount of air allowed through the air by-pass in the throttle body. This by-pass is enlarged or restricted, as an increase or decrease in engine idle speed is required, to meet varying engine operating conditions.

This results in a change in air/fuel ratio that alters the oxygen content of the exhaust gases as detected by the oxygen sensor. The SMEC then changes the amount of fuel introduced into the intake charge to maintain an optimum air/fuel ratio.

The SMEC monitors A/C operation and transaxle lever position. When necessary, the SMEC issues commands to the AIS to increase idle speed under these load conditions. With the air conditioning on and the throttle blade above a specific angle, the A/C cut-out relay prevents the air conditioning clutch from engaging until the throttle blade angle is reduced.

The A/C cut-out relay is wired in series with the A/C cycling clutch switch and A/C low pressure cut-out switch. This relay is normally closed during engine operation.

When the throttle is closed quickly after driving (sudden deceleration), engine stall (die-out) is prevented by increasing engine idle speed. This is an automatic function of the AIS motor through the SMEC.