Computers and Control Systems: Adjustments

NOTE: Adjustment of idle speed is usually not required. If idle speed is out of specification check and verify the operation of the idle speed control system. Refer to COMPUTERS AND CONTROL SYSTEMS.

Fig. 38 Connecting Tachometer:

INITIAL INSPECTION CONDITIONS:
^ Engine coolant temperature is 185 - 205°F.
^ Lights, cooling fan and all accessories are OFF.
^ Transmission is in neutral or park.
^ Steering wheel is in straight-ahead position.

ADJUSTMENT PROCEDURES
1. Check the ignition timing and adjust, if necessary. (Refer to procedure)
2. Loosen the accelerator cable, so a slight amount of slack is present.
3. Connect a digital voltmeter to the throttle position sensor leads. Probe into terminal 3 with the positive (+) probe and terminal 2 with the negative (-) probe.
4. Turn the ignition switch ON, but DO NOT start the engine.
5. Wait at least 15 seconds and check the ISC servo position. The voltmeter should register 0.9 volt. This is the initial position.

SC Motor Connector:

6. Turn the ignition switch OFF and disconnect the electrical connectors for the ISC servo. This will lock the idle speed control plunger at the initial position.
7. Open the throttle valve more than half-way, two or three times. Release the throttle valve and let it return with a click.

Fig. 37 Idle Speed Adjustment Screws (SAS):

8. Loosen the fixed speed adjusting screw (SAS) fully. Fig. 37

Tachometer Connector:

Tachometer Connection:

9. Connect a tachometer, start the engine and maintain idle speed.
10. Check that the idle speed is within specifications.

Basic Idle Speed:
750 ± 50 RPM

11. If idle speed is not as specified, adjust the ISC adjusting screw with a hexagon wrench.
12. Turn the fixed SAS in until the engine speed rises slightly.
13. Back-off the fixed SAS to the "touch point", where the engine speed ceases to decrease.
14. Back-off the SAS an additional half turn from the "touch point".
15. Stop the engine. Readjust the accelerator cable.
16. Reconnect the electrical connector for the idle speed control servo and remove the voltmeter from the engine.
17. With the ignition switch OFF, disconnect the negative battery terminal for at least 15 seconds. This will clear any diagnostic codes that may have occurred during testing.
18. Reconnect the battery, start the engine and check that the engine is operating in the normal idle range.