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. 21 Idle Speed Control (ISC) plunger adjustment specifications:

Preliminary Check
1. Check for an identification letter on ISC plunger, Fig. 21. If a letter appears, proceed to ``Adjustment Procedure.''
2. If no letter appears, remove plunger using tool J-29607 or equivalent, and measure distance from back of plunger head to end of plunger (dimension ``A''), Fig. 21. Record dimension for use in step 11 of ``Adjustment Procedure.''
3. Reinstall plunger, turning plunger in to a preset dimension that is less than dimension ``B,'' Fig. 21.

Fig. 22 Idle Speed Control (ISC) motor test connections:

Adjustment Procedure

1. Connect dwell meter to test lead in MC solenoid harness (usually a green wire) and set meter on 6 cylinder scale. Connect tachometer to engine following manufacturer's instructions.
2. Start engine and run at fast idle until it reaches normal operating temperature and dwell reading begins to fluctuate.
3. Stop engine and disconnect wiring harness connector to ISC motor. Do not connect or disconnect wiring harness connector to ILC motor with ignition in on position, as ECM will be damaged.
4. Using a jumper wire, connect battery voltage to terminal ``C'' on ISC motor, Fig. 22, then connect a jumper wire between terminal ``D'' and ground. Do not leave battery voltage connected to ISC motor longer than necessary to retract solenoid plunger. Do not connect battery voltage to terminals ``A'' or ``B'' on motor. ISC motor will be damaged if connections are improperly made.
5. Start engine and run until dwell reading begins to fluctuate. Place transmission in drive (manual transmission in neutral).

Fig. 23 Idle Speed Control (ISC) adjustment specifications:

6. With ISC plunger fully retracted, adjust idle speed to specified minimum authority RPM, Fig. 23, with throttle stop screw.
7. Place transmission in neutral and reverse jumper wire connections. Connect battery voltage to terminal ``D,'' then connect terminal ``C'' to ground. Leave jumper wires connected only long enough to fully extend ISC plunger.
8. With plunger fully extended, adjust idle speed to specified maximum authority RPM (manual transmission), Fig. 23, or 1500 RPM (automatic transmission), by turning ISC plunger with tool J-29607 or equivalent.
9. Place automatic transmission in drive and adjust idle speed to specified maximum authority RPM with ISC plunger. Adjustments must be made as quickly as possible. If engine RPM increases, adjustment cannot be performed, engine will have to be stopped and the procedure will have to be restarted from step 2.
10. Reconnect jumper wires as in step 7 and recheck maximum authority RPM. Motor will ratchet at full extension with voltage applied.

Fig. 21 Idle Speed Control (ISC) plunger adjustment specifications:

11. Remove jumper wires and measure dimension ``B,'' Fig. 21. Dimension must not exceed specifications shown in chart.
12. Connect jumper wires to ISC motor, as in step 4, to fully retract ISC plunger, then remove jumper wires.
13. Stop engine. Reconnect wiring harness connector to ISC motor. Test connections to ISC motor will cause ``Check Engine'' light to remain on until wiring harness is reconnected to motor. An intermittent trouble code will then be stored in the ECM memory which must be cleared.