Lanos S Hatchback L4-1.6L DOHC D-TEC MFI (1999)
Idle Air Control (IAC) Valve: Testing and Inspection
Idle Air Control System Check
Idle Air Control System Check
Circuit Description
The powertrain control module (PCM)/Engine control module (ECM) controls the engine idle speed with the idle air control (IAC) valve. To increase
the idle speed the PCM/ECM pulls the IAC pintle away from its seat, allowing more air to pass by the throttle bore. To decrease the idle speed, it
extends the IAC valve pintle toward its seat, reducing bypass air flow. A scan tool will read the PCM/ECM commands to the IAC valve in counts. The
higher counts indicate more air bypass (higher idle). The lower counts indicate less air is allowed to bypass (lower idle).
Diagnostic Aids
If the idle is too high, stop the engine. Fully extend the IAC valve with a IAC tester. Start the engine. If the idle speed is above 800 rpm, locate and
repair the vacuum leak. Also, check for a binding throttle plate or throttle linkage or an incorrect base idle setting.
