6000 V6-173 2.8L (1988)
Idle Speed/Throttle Actuator - Electronic: Testing and Inspection
The Electronic Control Module (ECM) moves the Idle Air Control (IAC) valve in small steps, called "counts." These can be measured by "Scan"
tool test equipment, which plugs into the Assembly Line Data Link (ALDL) connector.
If the IAC valve is disconnected and reconnected while the engine is running, the resulting idle rpm may be wrong and resetting of the IAC valve
will be required.
After running the engine, the IAC valve will reset when the ignition is turned "OFF." When servicing the IAC valve, it should only be
disconnected or connected with the ignition "OFF."
If the ECM is without battery power for any reason, the programmed position of the IAC valve pintle is lost, and replaced with a "default" value.
This causes the engine idle to be unstable for a period of approximately seven minutes. To return the lAC valve pintle to the correct position, see
"Idle Learn Procedure."
Different shaped pintles are used for different IAC valve applications. The Model B115 throttle body has an IAC valve with a 12 mm dual taper
pintle. Be sure to use the correct part number, with the correct pintle shape and diameter, when replacement is required.
The IAC valve affects only the idle characteristics of the vehicle. If it is fully retracted, too much air will be allowed into the manifold and idle
speed will be high. If it is stuck closed, too little air will be allowed in the manifold, and idle speed will be too low. If it is stuck part way open, the
idle may be rough, and will not respond to engine load changes. A Code 35 should set if a controlled idle cannot be maintained.
