Idle Air Control
Full details on the types of Toyota IACVs can be found here:
Two coil ISCV
The early type is a simple solanoid, called a Vacuum Switching Valve, which allows a vaccum to pass to a set of bellows that move against the throttle plate stop. They are triggered by ECU, or various electrical load switches.
Most people remove these when going to a stand-alone system, as they do not work very well after 25years of service.
The newer 20v engines have a Dual-Control Rotary Solanoid IAC System, marked as A on the picture below.
One coil opens the IAC valve, the other closes it, with neither coil active the IAC valve sits at 50%.
The document states:
''The ECM controls IACV positioning by applying a duty cycled signal to the two electrical coils in the IACV.
By changing the duty ratio (on time versus off time), a change in the magnetic field causes the valve to rotate.
Basically, as duty ratio drops belpw 50%, the valve closes the passage. If the IACV is disconnected or inoperative,
the valve will move to a default position and idle rpm will be around 1000 to 1200rpm at operating temperature.''
Thanks to the new Dual IAC firmware (1.0.30 on) and MembersPage/Skassa the Dual-Control Rotary Solanoid is now controlled correctly by VEMS. The following config values were used:
iac_conf=78 iac_max_steps=FF iac_tps_thres=08 iac_cold_idle_temp=A2 iac_warm_idle_temp=B4 iac_cold_rpm=96 iac_warm_rpm=82 iac_cold_start_pos=80 iac_warm_start_pos=66 iac_afterstart_rpm=23 iac_afterstart_duration=A0 iac_speed=06 iac_kp=6E iac_ki=03 iac_kd=FF