Throttle Body: Testing and Inspection

Note: Before performing minimum air flow test, make sure all accessories are off.

1. With vehicle in PARK (A/T) or NEUTRAL (M/T), START the engine and allow it to warm up until the cooling fan cycles at least once, then shut OFF the engine.
2. Connect a timing light and tachometer to the engine.

Note: When coolant temperature sensor is disconnected, the "Check Engine" light and cooling fan will turn on.

3. Disconnect the coolant temperature sensor and START engine. Adjust basic timing to 12° BTDC ± 2°, then shut OFF the engine and connect coolant temperature sensor.
4. Disconnect the 3/16" manifold vacuum purge line from the top of the throttle body and cap the throttle body nipple.
5. Remove PCV valve and attach metered orifice no. 6457 (or equivalent 0.125 inch orifice) to intake manifold nipple.
6. 5. Connect scan tool, START engine and allow to idle for at least one minute.
7. Using scan tool, access Minimum Air Flow Idle Speed function. The following should occur:
a. Idle Air Control (IAC) motor will fully close.
b. Idle spark advance will become fixed.
c. Engine rpm will be displayed on scan tool.
8. Confirm idle rpm with tachometer. If idle speed is not within the range below, replace throttle body. SEE Powertrain Management/Fuel Delivery and Air Induction/Throttle Body/Service and Repair

Idle Speed-During Minimum Airflow Test
Less than 1,000 miles on vehicle 700-1,300 rpm
Over 1,000 miles on vehicle 1,100-1,300 rpm

9. Shut OFF engine; remove metered orifice, install PCV valve, scan tool, and tachometer. Connect purge line to throttle body.
10. Erase any fault codes that may have been set.

Note: If vehicle passes minimum airflow test, and still exhibits idle speed problems, perform Idle Air Control (IAC) motor actuation test using scan tool.