Idle Speed Adjustments

1. Start the engine and enter diagnostics. Select PCM/ECM Override E.5.3, ISC Motor.

2. Press the cooler button to retract the ISC motor. The fuel data center will display E.5.3 and 00 alternately. The ISC motor will slowly retract (about 20 seconds) to a fully retracted position. Steady spark advance is provided during retracts. Verify that the throttle lever is resting on the minimum idle speed screw. With ISC plunger fully retracted, disconnect ISC harness. If the engine stalls at this point, go to step 6.

3. With the ISC fully retracted, the plunger should not be touching the throttle lever. If contact is noted, adjust the ISC plunger (turn in) with pliers or available special tool J-29607 so that it is not touching the throttle lever. Make sure that the throttle is not being bound by the cruise, TV, or throttle cables. Readjust or repair cables if holding the throttle open.

4. Connect a tachometer and check the minimum idle speed. If the minimum idle speed is outside of the following limits, adjust the minimum idle speed screw to obtain the idle speed specified in MECHANICAL SPECIFICATIONS. Use an average reading of rpm to check minimum idle rpm refer to MECHANICAL SPECIFICATIONS.

5. If engine speed is not within the above limits, check for vacuum leaks at the throttle body, intake manifold, vacuum fittings, tees and hoses. If the minimum air setting is made with a vacuum leak present, fuel control can be adversely affected throughout the driving range.

6. If the engine stalled at minimum air (ISC fully retracted), check the throttle blades for deposits that might restrict air flow. If there are deposits, clean the primary throttle bore and the area behind and around the throttle plate. Return to step one after cleaning the throttle body.

ISC SOLENOID

1. With key on engine off, select the ISC motor override E.5.3. Press the warmer button on the ECC. The fuel data center should display E.5.3 and 99 alternately indicating that indicating that the override function has started. The ISC will extend to the maximum extended position.

2. With the ISC fully extended, the TPS voltage should be between 1.15 and 1.20 volts. If the TPS is not within this range, adjust the ISC Plunger as follows:

^ TPS below 1.15 volts.

- Adjust the ISC plunger out by turning the plunger counterclockwise until the TPS parameter reads 1.18 volts.

^ TPS above 1.20 volts.

- Adjust the ISC plunger in be turning the plunger clockwise until the TPS parameter reads 1.18 volts.

3. Recheck the max extend setting, press the cooler button to retract the ISC plunger, wait 5 seconds. Press the warmer button and read the TPS voltage. Readjust the ISC plunger if necessary.

*** UPDATED BY TSB #91-I-11 DATE: 10/90

IDLE LEARN PROCEDURE

Idle learn is used during coast down to compensate for loss of air flow due to throttle body deposits. If the battery is disconnected for a service procedure or any other reason, the learned value for the idle throttle angel offset is lost. The reset procedure allows the idle learn routine to seek and retain the proper throttle angel for each particular throttle body condition. This decreases the potential for stalling during coast down.

Before performing the reset procedure all service procedures must be complete., and the engine must be running continuously for a minimum of 18 minutes on 1990 vehicles, and 13 minutes on 1991 vehicles.

Reset procedure:

1. Place the vehicle transmission in drive wither the brakes applied.
2. Place vehicle climate control in the OFF position and allow the engine to remain at IDLE for at least one minute.
3. Make sure the outside air temperature reading is at least 50°F. Place the vehicle climate control in the AUTO position, verify A/C clutch engagement, and allow the engine to remain at IDLE for at least one minute.
4. Place the3 transmission in Park and turn off the ignition.

IMPORTANT: Because of the load differences on the engine with A/C on versus A/C off, it is very important than learning be allowed under both conditions.