Idle Speed Adjustments
Diagnostic Flow Diagram - Part 1 Of 3:
Diagnostic Flow Diagram - Part 2 Of 3:
Diagnostic Flow Diagram - Part 3 Of 3:
NOTE: This adjustment should ONLY be performed when the throttle body has been replaced or when required to do so by diagnostic procedures. Engine should be at normal operating temperature before making any adjustment.
If the engine idle speed is not within the above limits (too high), 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 all driving ranges.
The minimum idle speed screw, used to regulate the minimum idle speed of the engine is pre-adjusted at the factory. If it is necessary to adjust the minimum idle speed screw, use tool J-38457 or equivalent.
Electronic Climate Control (ECC) Panel:
MINIMUM AIR ADJUSTMENT
1. Visually check all vacuum hoses for splits, leaks or cuts. Repair as needed.
2. Start the engine. Enter diagnostics and select PCM data P.0.4 (Coolant Temperature). Operate the engine until coolant temperature is greater than 95°C.
3. Exit Diagnostics. Select the "OFF" mode on ECC. Place the steering wheel in the center, straight ahead position. Transmission should be in "PARK". Disable the generator by grounding the green harness connector plug adjacent to the generator.
4. Check ignition timing. Enter set timing mode by jumpering pin A to B an the ALDL connector. Check for timing at 10° or 6° BTDC if regular fuel is used. Adjust if necessary. Disconnect the jumper at the ALDL after the timing is verified as correct.
5. Enter diagnostics and select PCM override E.5.3 (ISC Motor).
6. Press the "COOLER" button on the ECC to retract the ISC motor. This action will disengage the A/C compressor and command EGR "OFF". The ECC display will change from '50' to '00'. The ISC motor will retract slowly to a fully retracted position. Verify that the throttle lever is resting on the minimum idle speed screw. With the ISC plunger fully retracted, disconnect the ISC harness. If the engine stalled at minimum air (ISC retracted), check the throttle blades for deposits that might restrict air flow. If there are deposits, clean the throttle bores and the area behind and around the throttle plates.
7. 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 so that it is not touching the throttle lever. The throttle lever must be resting on the minimum air screw. Make sure that the throttle is not being bound by the throttle, cruise, or TV cables.
8. Check the minimum idle speed displayed on the Driver Information Center (DIC). Use an average reading of rpm to check minimum idle rpm.
^ For vehicles with 0-500 odometer miles:
- Minimum idle rpm should be 450-500 rpm.
^ For vehicles with more that 500 odometer miles:
- Minimum idle rpm should be 500-550 rpm.
9. If the minimum idle speed is out of limits, use tool J-38457 to adjust the minimum idle screw to obtain the following idle speed
^ For vehicles with 0-500 odometer miles:
- Set Minimum idle rpm to 475 rpm.
^ For vehicles with more that 500 odometer miles:
- Set Minimum idle rpm to 525 rpm.
NOTE: If the idle speed cannot be corrected, check that the throttle is not held off the minimum idle speed screw because of linkage or cable binding. Also, check for leaking vacuum hoses or air leaks at the throttle body or intake manifold.
10. Remove the generator disable ground wire. If minimum idle speed was adjusted, adjust the TPS.
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 angle offset is lost. The reset procedure allows the idle learn routine to seek and retain the proper throttle angle 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 coolant temperature must be greater than 80°C. This takes about 8 minutes.
Reset procedure:
1. Warm engine until operating temperature is reached. Coolant temperature must be greater than 80°C. This takes about 8 minutes.
2. Enter diagnostics. Turn the ignition "OFF". Allow approximately 20 seconds for the ISC motor to retract and perform a "TPS Learn". Repeat this step.
3. Place the vehicle transmission in drive with the brakes applied.
4. Place vehicle climate control in the "OFF" position and allow the engine to remain at IDLE for at least one minute.
5. 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.
6. Place the 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.