Engine Performance - Hard Starting, Poor Driveability,
Bulletin No. 025/92Issued 7/21/92
Revised
Category
F
Applicable Model/s
1991-92 Navajo
Subject:
THROTTLE BODY CLEANING
DESCRIPTION
Sludge deposits or oil film on the throttle body bore and plate, or on the idle air bypass valve may cause one or more of the following symptoms:
- Hard cold start
- Stall on initial startup
- Stall during idle
- Stall during deceleration
- Rough idle
- Rolling idle
- Hesitation during acceleration
INSPECTION AND REPAIR PROCEDURE
If the vehicle was built before 1/1/91 and has a VIN lower than 4F2CU44X*MUM08524, follow the Idle Air Adjustment Spacer Kit Installation and Idle Speed Adjustment procedures. Do not clean the throttle body.
If the vehicle was built after 1/1/91 and has a VIN of 4F2CU44X*MUM08524 or higher, then only the Idle Air Bypass Valve Cleaning procedure should be followed.
Idle Air Adjustment Spacer Kit Installation
Note:
Verify that the following areas are not causing the idle quality concern before proceeding with kit installation:
- Contamination within the idle air bypass solenoid
- Lack of fuel system control (excessively rich or lean)
- Throttle sticking or binding
- Ignition timing change
- Malfunctioning cooling system
- Vacuum leaks (air intake manifold, vacuum hoses, vacuum reservoirs, power brake booster)
- Service codes are set, indicating that the EEC system detects a fault
If any of the above mentioned areas are found to be at fault, correct them before proceeding with the kit installation.
The idle air adjustment spacer kit (Part no. ZZL0 FF 013) is used to correct sludge contamination of the throttle bore and plate only. If the vehicle being serviced already has an adjustment spacer installed, verify the spacer for proper adjustments in steps 3 and 9 only (replacing the spacer kit is not required). If the throttle body being serviced is identified as a sludge tolerant design (yellow and black attention label), this procedure is not required.
1. Turn the engine off, put the transmission in park, engage the parking brake and block the wheels. Disconnect all cables from the throttle control arm and disconnect the Idle Air Speed (IASP) solenoid connector.
2. Do not clean the throttle bore/plate area. Removing the sludge accumulation in the throttle bore will reduce the effectiveness of the idle air adjustment spacer.
3. Adjust the throttle plate position in the throttle bore to minimize closed plate air flow. This is done by turning the throttle plate stop screw on the throttle body counterclockwise until it is no longer in contact with the throttle control arm stop. Gently cycle the throttle plate open and closed a few times to ensure that the throttle plate is at the fully closed position. Place a 0.002" feeler gauge between the stop screw and the throttle control arm and turn the screw clockwise until it contacts the feeler gauge. Remove the feeler gauge and turn the screw clockwise an additional 1/2 turn.
4. Snap the throttle from open to closed several times to make sure that the throttle plate does not stick. If the throttle plate sticks, turn the screw slowly clockwise to eliminate the stick/bind/grab condition. Run the Key On/Engine Off (KOEO) self test to verify that no throttle position sensor (TPS) fault codes exist once the throttle plate position adjustment is completed. If any codes are present, repair as necessary.
5. Remove the IASP solenoid and discard the old gasket. Note the position of the solenoid connector before removing it, so it can be replaced with the same orientation.
6. Install the idle air adjustment spacer between the IASP solenoid and the engine mounting location. Figure 1.
IMPORTANT:
Install the spacer so that the spacer keyway part aligns with the clean air port of the mount.
7. Torque the bolts to 8-11.5 N-m (6 - 8.5 ft.lbs.)
8. Reconnect the cables to the throttle control arm.
9. To adjust the idle speed, do not turn the throttle plate stop screw. Instead, turn one or both spacer trim screws using a 2.5 mm allen wrench (turn clockwise to decrease rpm and counterclockwise to increase rpm).
10. Reconnect the connector to the IASP solenoid. Verify that the engine is idling properly.
11. With the engine running, cycle the throttle several times to verify that the plate does not stick, bind, or grab (repeat steps 4 and 9 if there is a stick, bind or grab).
12. Apply the "Attention" sticker, provided with the kit, to the IASP solenoid wire/harness lead (Figure 1) once all adjustments are completed.
13. Run the Key On Engine Running/Key On Engine Off (KOER/KOEO) EEC engine self tests and correct any fault codes that may exist.
WARNING:
Before proceeding with the idle speed adjust procedure, verify that the following conditions exist:
- Transmission is in park or neutral
- Parking brake is applied
- Wheels are blocked
- Engine is at operating temperature
- Heater, A/C, and other accessories are off
Idle Speed Adjustment
1. With the engine off, disconnect the negative battery terminal for 5 minutes then reconnect the battery.
2. D-isconnect the idle air bypass solenoid connection
3. Start the engine and run it at 2500 rpm for 30 seconds.
4. Place the transmission in park (automatic transmission) or neutral (manual transmission).
5. Check/adjust idle rpm, turn the service spacer trim screw to 675 rpm.
6. Shut off the engine and disconnect the negative battery terminal for 5 minutes, then reconnect the battery.
7. With the engine off, reconnect the idle air bypass solenoid connector.
8. Start the engine and allow it to stabilize for 2 minutes. Rev the engine and let it return to idle.
Idle Air Bypass Valve Cleaning
WARNING:
This cleaning procedure should be used with sludge tolerant throttle bodies which are identified with a yellow/black attention label and those using service kit ZZL0 FF 013. No attempt should be made to clean the throttle body bore/plate area by direct spraying or scrubbing.
1. Remove the air bypass valve from the upper manifold assembly (see Workshop Manual, Section F-02).
2. Remove the electrical solenoid assembly from the mechanical portion of the air bypass valve by removing the two screws, then sliding the mechanical portion away from the solenoid.
3. Soak the mechanical portion in an appropriate carburetor cleaner for a maximum of 2 to 3 minutes.
CAUTION:
Do not exceed 3 minutes soak time and do not use choke cleaner because the internal O-ring may deteriorate.
4. With the mechanical portion completely submerged in cleaner, agitate it in all directions.
5. Push in on the rod that mates with the solenoid assembly. Agitate in all directions with the unit submerged and the rod held in as far as possible.
6. Remove the unit from the cleaning fluid and dry it using shop air.
7. Reassemble the air bypass valve and install it on the manifold.
PARTS INFORMATION
WARRANTY INFORMATION
(Applies to vehicles covered under warranty.)