S15/T15 2WD Jimmy V6-262 4.3L (1991)
Idle Speed: Adjustments
Idle Speed and Minimum Air Rate
NOTE: Before performing this check, there should be no codes displayed, idle air control system has been checked and ignition timing correct.
CONTROLLED IDLE SPEED CHECK
1.
Set parking brake and block drive wheels.
2.
Connect a "SCAN" tool to the ALDL connector 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 specification chart for controlled idle speed and IAC valve pintle positions counts. See: Powertrain Management/Computers and Control
Systems/Specifications
6.
If within specifications, the idle speed is being controlled correctly by the ECM/PCM.
7.
If not within specifications, refer to STALLS/ROUGH, UNSTABLE OR INCORRECT IDLE, under DIAGNOSIS BY SYMPTOM.
Stop Screw Plug Removal
NOTE: DO NOT attempt to adjust the minimum idle air rate unless the throttle body has been rebuilt or replaced. Incorrect idle speeds are usually
caused by a dirty throttle plate or a vacuum leak.
MINIMUM IDLE AIR RATE CHECK
1.
Check controlled idle speed and perform idle air control system check first.
2.
Set parking brake and block drive wheels.
3.
Start engine and bring it to normal operating conditions. Turn engine "OFF".
4.
Remove air cleaner, adapter and gaskets. On ST series models leave THERMAC hose connected. Check that the throttle lever is not being bound
by the throttle, TV or cruise control cables.
5.
With IAC valve connected, ground the diagnostic terminal (ALDL) connector.
6.
Turn "ON" ignition, do not start engine. Wait at least 45 seconds.
7.
With ignition "ON", engine stopped, test terminal still grounded, disconnect IAC valve electrical connector. Care should be taken to make sure
connector is pulled straight out so that the moment of electrical disconnect is the same for all pins. Remove ground from the ALDL connector.
8.
Connect a SCAN tool to the ALDL connector and place in open mode.
9.
Start engine. With transmission in neutral, allow engine rpm to stabilize.
10.
Check rpm against specification chart. Disregard IAC counts on "SCAN" tool with IAC valve disconnected. If the engine has less than 500 miles
on it or is checked at altitudes above 1500 feet, the idle rpm should be lower than the specifications chart list, with IAC valve fully seated. See:
Specifications
11.
If the minimum idle air rate is within the 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 stop screw plug by piercing it with an awl, then applying leverage.
14.
With engine at normal operating conditions, adjust stop screw to obtain nominal rpm specifications with seated IAC valve. Check to make sure
Throttle Position Sensor is adjusted properly. See: Powertrain Management/Computers and Control Systems/Sensors and Switches - Computers
and Control Systems/Throttle Position Sensor
15.
Turn ignition "OFF" and reconnect the IAC valve electrical connector.
16.
Disconnect the "SCAN" tool.
17.
Use silicon sealant or equivalent to cover stop screw hole.
18.
Install air cleaner, adapter and gasket.
19.
Reset Idle Air control motor by turning key "ON" for ten seconds then "OFF."
IAC RESET PROCEDURE
1.
Depress accelerator pedal slightly.
2.
Start and run engine for 5 seconds.
3.
Turn ignition "OFF" for 10 seconds.
4.
Restart engine and check for proper idle operation.
