Idle Speed/Throttle Actuator - Electronic: Description and Operation

TBI 220 Air Flow Diagram:

TBI 220 Fuel Flow Diagram:

Engine idle speeds are controlled by the ECM through the Idle Air Control (IAC) valve mounted on the throttle body. The ECM sends voltage pulses to the IAC motor windings causing the IAC motor shaft to move in and out a given distance for each pulse, (referred to as IAC counts on a scan tool). This movement controls airflow around the throttle plates, which in turn, controls engine idle speed, either cold or hot. IAC valve pintle position counts can be seen by using a Scan tool. 0 counts corresponds to fully closed passage, while 140 counts or more (depending on application) corresponds to full flow. While the IAC valve controls airflow through the throttle body, (and thus idle speed) a minimum amount of air flow goes past the throttle plates. The throttle plate position is set and plugged at the factory and should not normally be adjusted.