K 1500 Truck 4WD V8-454 7.4L (1988)
Idle Speed: Adjustments
Minimum Air Rate - Fuel Injection Only
*** UPDATED BY TSB # 88T556E DATED NOV. 1987
CONTROLLED IDLE SPEED CHECK
1.
Set parking brake and block drive wheels.
2.
Connect a SCAN tool to the assembly line data link (ALDL) connect with tool in Open Mode.
3.
START engine and bring it to normal operating temperature.
4.
Check for correct state of PARK/NEUTRAL switch on SCAN tool.
5.
Check specifications chart for controlled idle speed and IAC valve pintle position (counts).
6.
If within specifications, the idle speed is being correctly controlled by the ECM.
7.
If not within specifications, perform MINIMUM IDLE AIR RATE CHECK. If still not within specifications, See: Powertrain
Management/Computers and Control Systems/Testing and Inspection
MINIMUM IDLE AIR RATE CHECK
1.
Check controlled idle speed and perform idle air control check first.
2.
Set parking brake and block drive wheels.
3.
START engine and bring it to normal operating temperatures 185-212 degrees Fahrenheit (85-100 degrees Celsius). Turn engine OFF.
4.
Remove air cleaner, adapter and gaskets. Check that the throttle lever is not being bound by the throttle, throttle valve or cruise control cables.
5.
With IAC valve connected, ground the diagnostic terminal (ALDL).
6.
Turn ON ignition, DO NOT START engine. Wait at least 10 seconds (this will allow the IAC pintle to extend and seat in the throttle body.).
7.
With ignition ON, engine stopped, test terminal still grounded, disconnect IAC valve electrical connector. (This disables the IAC valve in the
seated position). Remove the ground from the diagnostic terminal.
8.
Connect a SCAN tool to the ALDL connector and place in open mode. If a tool is not available connect a tachometer to the engine.
9.
START engine. With transmission in NEUTRAL, allow engine rpm to stabilize.
10.
Check rpm against specifications. Disregard IAC counts on SCAN tool with the IAC disconnected. If the engine has less than 500 miles or is
checked at altitudes above 1500 feet, the idle rpm with a seated IAC valve should be lower than values in chart.
11.
If the minimum idle air rate is within specifications, no further check is required.
12.
If the minimum idle air rate is not within specifications, perform the following procedures:
13.
If present, remove the stop screw plug by piercing it with an awl, then applying leverage. The screw is covered to discourage unauthorized
adjustments.
14.
With the engine at normal operating temperature 185-212 degrees Fahrenheit (85-100 degrees Celsius), adjust stop screw to obtain nominal rpm
per specifications with seated IAC valve.
15.
Turn ignition OFF and reconnect IAC valve electrical connector.
16.
Disconnect the SCAN tool or tachometer.
17.
Use silicon sealant or equivalent to cover stop screw hole.
18.
Install air cleaner, adapter and gasket.
CONTROLLED IDLE SPEED
