GM Astro/Safari 1985-1996 Repair Guide

Throttle Body

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See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: Operation of the TBI unit-Model 300



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Fig. Fig. 2: Exploded view of the Model 300 throttle body-2.5L engine



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Fig. Fig. 3: Exploded view of the Model 220 throttle body-4.3L engine



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Fig. Fig. 4: Operation of the TBI unit-Model 700



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Fig. Fig. 5: Exploded view of the Model 700 throttle body-2.5L engine

The Model 300 throttle body, used on the 2.5L engine (1985-87), is a single barrel, single injector type. The 1988-90 2.5L engine is equipped with a model 700 single barrel, single injector type. The Model 220 throttle body, used on the 4.3L engine (1986-on), is a dual barrel, twin injector type. The operation of all three types are basically the same. This system is not to be confused with the direct port injection Central Multiport Fuel Injection (CMFI) or Central Sequential Multiport Fuel Injection (CSFI) systems.

Both throttle bodies are constantly monitored by the ECM to produce a 14.7:1 air/fuel ratio, which is vital to the catalytic converter operation.

REMOVAL & INSTALLATION



See Figures 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15



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Fig. Fig. 6: Replacing the throttle body-2.5L engine



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Fig. Fig. 7: Replacing the throttle body-4.3L engine



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Fig. Fig. 8: Both the throttle cable and the cruise control linkage need to removed



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Fig. Fig. 9: Use a backup wrench and a flare wrench when disconnection the fuel lines



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Fig. Fig. 10: Some fuel may spill out of the line connections, so place a rag under the fittings to catch it



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Fig. Fig. 11: Always replace the fuel line O-rings



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Fig. Fig. 12: Remove the 3 bolts holding the throttle body



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Fig. Fig. 13: Lift the throttle body straight up and be careful not to drop anything into the manifold



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Fig. Fig. 14: Slide the electrical connection from the groove



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Fig. Fig. 15: Always replace the throttle body base gasket, otherwise a vacuum leak may occur


CAUTION
Before removing any component of the fuel system, be sure to reduce the fuel pressure in the system. The pressure regulator contains an orifice in the fuel system; when the engine is turned Off, the pressure in the system will bleed down within a few minutes.

  1. Relieve the pressure in the fuel system.
  2.  
  3. Remove the air cleaner. Disconnect the negative battery cable from the battery.
  4.  
  5. Disconnect the electrical connectors from the idle air control valve, the throttle position sensor and the fuel injector(s).
  6.  
  7. Remove the throttle return spring(s), the cruise control (if equipped) and the throttle linkage.
  8.  
  9. Label and disconnect the vacuum hoses from the throttle body.
  10.  
  11. Place a rag (to catch the excess fuel) under the fuel line-to-throttle body connection, then disconnect the fuel line from the throttle body.
  12.  
  13. Remove the attaching hardware, the throttle body-to-intake manifold bolts, the throttle body and the gasket.
  14.  

Be sure to place a cloth in the intake manifold to prevent dirt from entering the engine.

  1. Using a gasket remover (if necessary), clean the gasket mounting surfaces.
  2.  

To install:
  1. Use a new gasket. Install the gasket, throttle body and mounting bolts. Torque the throttle body-to-intake manifold nuts/bolts to 13 ft. lbs. (17 Nm).
  2.  
  3. Connect the fuel lines to the throttle body.
  4.  
  5. Connect the vacuum hoses to the throttle body.
  6.  
  7. Install the throttle return spring(s), the cruise control (if equipped) and the throttle linkage.
  8.  
  9. Depress the accelerator pedal to the floor and release it, to see if the pedal returns freely.
  10.  
  11. Connect the electrical connectors to the idle air control valve, the throttle position sensor and the fuel injector(s).
  12.  
  13. Install the air cleaner. Connect the negative battery cable to the battery.
  14.  
  15. Start the engine, check for leaks and proper operation.
  16.  

ADJUSTMENTS



Idle Speed and Mixture
1985-87 2.5L ENGINE

See Figure 16



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Fig. Fig. 16: Installing tool J-33047 to adjust the idle speed-Model 300

The following procedures require the use a tachometer, GM tool No. J-33047 or equivalent, GM Torx® Bit No. 20, silicone sealant, a5/32in. drill bit, a prick punch and a1/16in. pin punch.

The throttle stop screw, used in regulating the minimum idle speed, is adjusted at the factory and is not necessary to perform. This adjustment should be performed ONLY when the throttle body has been replaced.

The factory supplied replacement throttle body assembly will have the minimum idle adjusted at the factory.

  1. Remove the air cleaner and the gasket. Be sure to plug the THERMAC vacuum port (air cleaner vacuum line-to-throttle body) on the throttle body.
  2.  
  3. Remove the throttle valve cable from the throttle control bracket to provide access to the minimum air adjustment screw.
  4.  
  5. Using the manufacturer's instructions, connect a tachometer to the engine.
  6.  
  7. Remove the electrical connector from the Idle Air Control (IAC) valve, located on the throttle body.
  8.  
  9. To remove the throttle stop screw cover, perform the following procedures:
    1. Using a prick punch, mark the housing at the top over the center line of the throttle stop screw.
    2.  
    3. Using a 5 / 32 in. drill bit, drill (on an angle) a hole through the casting to the hardened cover.
    4.  
    5. Using a 1 / 16 in. pin punch, place it through the hole and drive out the cover to expose the throttle stop screw.
    6.  

  10.  
  11. Place the transmission in Park (AT) or Neutral (MT), start the engine and allow the idle speed to stabilize.
  12.  
  13. Using the GM tool No. J-33047 or equivalent, install it into the idle air passage of the throttle body; be sure that the tool is fully seated in the opening and no air leaks exist.
  14.  
  15. Using the GM Torx® Bit No. 20, turn the throttle stop screw until the engine speed is 475-525 rpm (AT in Park or Neutral) or 750-800 rpm (MT in Neutral).
  16.  
  17. With the idle speed adjusted, stop the engine, remove the tool No. J-33047 from the throttle body.
  18.  
  19. Reconnect the Idle Air Control (IAC) electrical connector.
  20.  
  21. Using silicone sealant or equivalent, cover the throttle stop screw.
  22.  
  23. Reinstall the gasket and the air cleaner assembly.
  24.  

1985-87 4.3L ENGINE

The following procedure requires the use of a tachometer, a prick punch, a5/32in. drill bit, a1/16in. pin punch, a grounding wire and silicone sealant.

  1. Remove the air cleaner and the gasket.
  2.  
  3. Remove the throttle stop screw cover by performing the following procedures:
    1. Using a prick punch, mark the housing at the top over the center line of the throttle stop screw.
    2.  
    3. Using a 5 / 32 in. drill bit, drill (on an angle) a hole through the casting to the hardened cover.
    4.  
    5. Using a 1 / 16 in. pin punch, place it through the hole and drive out the cover to expose the throttle stop screw.
    6.  

  4.  

The following adjustment should be performed ONLY when the throttle body assembly has been replaced; the engine should be at normal operating temperatures before making this adjustment.

  1. With the Idle Air Control (IAC) connected, ground the diagnostic terminal of the Assembly Line Communications Link (ALCL) connector.
  2.  

The Assembly Line Communications Link (ALCL) connector is located in the engine compartment on the left side firewall.

  1. Turn the ignition switch ON but DO NOT start the engine. Wait 30 seconds, this will allow the IAC valve pintle to extend and seat in the throttle body.
  2.  
  3. With the ignition switch turned On, disconnect the Idle Air Control (IAC) valve electrical connector.
  4.  
  5. Remove the ground from the Diagnostic Terminal ALCL connector and start the engine.
  6.  
  7. Adjust the idle stop screw to obtain 400-450 rpm (AT in Drive).
  8.  
  9. Turn the ignition OFF and reconnect the IAC valve electrical connector.
  10.  
  11. Using silicone sealant or equivalent, cover the throttle stop screw.
  12.  
  13. Reinstall the gasket and the air cleaner assembly.
  14.  

1988-90 2.5L AND 1988-on 4.3L ENGINES

See Figure 17



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Fig. Fig. 17: Removing the idle stop screw plug-Model 700

Before performing this check, there should be no codes displayed, idle air control system has been checked and ignition timing is correct.

  1. CONTROLLED IDLE SPEED CHECK: set the parking brake and block the wheels.
  2.  
  3. Connect a SCAN tool to the ALDL connector with the tool in the OPEN MODE.
  4.  
  5. Start the engine and bring it to normal operating temperature.
  6.  
  7. Check for correct state of Park/Neutral switch on the SCAN tool.
  8.  
  9. If the idle and IAC counts are not within specifications:

    2.5L MT in NEUTRAL 800 rpm, 5-20 IAC valve counts and in the closed loop.
     
    2.5L AT in DRIVE 750 rpm, 5-20 IAC valve counts and in the closed loop.
     
    4.3L MT in NEUTRAL 500-550 rpm, 2-12 IAC valve counts and in the closed loop.
     
    4.3L AT in DRIVE 500-550 rpm, 10-25 IAC valve counts and in the closed loop.
     

  10.  
  11. MINIMUM IDLE AIR RATE CHECK: check the controlled idle speed and perform the idle air control system check first.
  12.  
  13. With the IAC valve connected, ground the diagnostic A and B terminals of the ALDL connector.
  14.  
  15. Turn ON the ignition with engine NOT running, wait for ten seconds to allow the IAC valve to stabilize. Remove the ground from the ALDL and disconnect the IAC valve.
  16.  
  17. Connect the SCAN tool to the ALDL connector and place in the open mode. If a SCAN tool is not available, connect a tachometer to the engine.
  18.  
  19. Start the engine and allow to stabilize.
  20.  
  21. Check the rpm using the specifications.
  22.  
  23. If the minimum idle rate is not within specifications perform the following:
    1. Remove the idle stop screw plug by piercing it with an awl, then apply leverage to remove the plug.
    2.  
    3. Adjust the screw to the specified rpm.
    4.  
    5. Turn the engine OFF, disconnect the SCAN tool, reconnect the IAC valve and cover the idle stop screw with silicone sealer.
    6.  

  24.  
  25. Install the air cleaner, adapter and gasket.
  26.  

 
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