Monitor Description

Fig 1: Engine Idling Speed And Learned IAC Valve Angle Value Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

The IAC valve controls the volume of air that bypasses the throttle valve.

Idling speed is determined by the volume of air that passes through the Intake Air Control (IAC) valve. When the volume is large, the idling speed increases. Conversely, when it is small, the idling speed decreases. The ECM sends a duty signal to the IAC valve and drives the IAC valve motor to regulate this air volume. If any of the following conditions apply, the ECM determines that the IAC system is malfunctioning, and illuminates the MIL and sets a DTC: the actual engine idling speed does not reach the target idling speed, the IAC learned valve angle remains at the maximum or minimum, or the duty ratio signal to the IAC valve is stuck.

Example:

The ECM sets DTC P0505 if either of the following conditions applies:

• The difference between the actual and target engine idling speeds exceeds 200* rpm while the engine is idling, and this occurs 5 times.
• The IAC learned valve angle remains at the maximum or minimum for 5 seconds.

The ECM sets DTC P0511 (open/short circuit) if the following condition applies:

• The duty ratio signal to the IAC valve is stuck at 0 % or 100 %.

  *: The threshold varies according to engine load.