Idle Speed Control (ISC)

Do not use ISC plunger to adjust curb idle speed, as idle speed is controlled by the Electronic Control Module (ECM). When a new ISC is installed or when indicated by the ``System Performance Check,'' a base (minimum authority) and a high (maximum authority) RPM check must be made and adjustments performed as needed. When making low and high speed adjustments, low speed adjustment must be performed first.

Fig. 10 Idle speed control (ISC) plunger adjustment specifications:

Preliminary Check

1. Check ISC plunger for an identification letter as shown, Fig. 10. If letter appears, proceed to ``Adjustment Procedure.''
2. If letter does not appear, remove plunger using tool No. J-29607 or equivalent, then measure distance from back of plunger head to plunger end (dimension A), Fig. 10. Record dimension for use during ``Adjustment Procedure.''
3. Reinstall plunger to a dimension less than dimension B, Fig. 10.

Fig. 10 Idle speed control (ISC) plunger adjustment specifications:

Fig. 11 Idle speed control (ISC) motor test connections:

Fig. 12 Idle speed control (ISC) adjustment specifications:

Adjustment Procedure

1. Connect a tachometer to engine. If vehicle is equipped with tachometer, connect remote tachometer to distributor side of tach filter.
2. Connect dwell meter to MC solenoid dwell lead, then set meter to 6 cylinder scale.
3. Start engine and run at fast idle until engine reaches normal operating temperature and dwell readings start to fluctuate.
4. Turn off ignition, then disconnect ISC motor connector.
5. Apply battery voltage to terminal C of ISC motor connector to retract plunger, Fig. 11, then ground terminal D. Do not leave battery voltage connected to ISC motor longer than necessary to retract plunger. Do not connect battery voltage to terminals A or B on motor. ISC motor will be damaged if connections are improperly made.
6. Start engine and run until dwell reading begins to fluctuate, then place automatic transmissions in Drive (manual transmission in Neutral).
7. With ISC plunger fully retracted, adjust idle speed to specified minimum authority RPM, Fig. 12, using throttle stop screw.
8. Place automatic transmission in Park, manual transmission in Neutral, then reverse jumper wire connections. Apply battery voltage to terminal D, then ground terminal C. Only leave jumper wires connected long enough to extend ISC plunger.
9. On vehicles with manual transmission, adjust idle speed to specified maximum authority RPM, Fig. 12, by turning ISC plunger using tool No. J-29607 or equivalent.
10. On vehicles with automatic transmission, adjust idle speed to specified maximum authority RPM, Fig. 12, by turning ISC plunger using tool No. J-29607 or equivalent.
11. On all vehicles, recheck ISC maximum authority adjustment RPM with battery voltage applied to motor. Motor will ratchet at full extension with power applied.
12. Measure distance from back of plunger head to ISC nose piece, dimension B, Fig. 10. Dimension must not exceed specification shown in chart.
13. Fully retract ISC plunger, then place automatic transmission in Park, manual transmission in Neutral and turn off ignition. Disconnect 12 volt power source, ground lead, tachometer and dwell meter. Connect four terminal harness to ISC motor. This procedure will cause the Check Engine lamp to light and an ISC motor trouble code to be set. Restoring the system to normal operation will cause the lamp to go out, but the trouble code will continue to be stored as an intermittent problem. To clear diagnostic trouble code, remove ECM fuse from fuse panel or disconnect battery ground cable for approximately 10 seconds.