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    GM Full Size Vans 1987-1997 Repair Guide

    Throttle Body

    Print

    See Figure 1



    Click image to see an enlarged view

    Fig. Fig. 1: Exploded view of the model 220 TBI unit

    The Model 220 throttle body assembly consists of three major casting assemblies:



    Fuel pressure cover with pressure regulator.
     
    Fuel metering body with fuel injectors.
     
    Throttle body with an Idle Air Control (IAC) valve and a Throttle Position (TP) sensor.
     

    The Throttle Position (TP) sensor is a variable resistor used to convert the degree of throttle plate opening to an electrical signal to the computer control module. The module uses this signal as a reference point of throttle valve position. In addition, an Idle Air Control (IAC) assembly, mounted in the throttle body is used to control idle speeds. A cone-shaped valve in the IAC assembly is located in an air passage in the throttle body that leads from the point beneath the air cleaner to below the throttle valve. The module monitors idle speeds and, depending on engine load, moves the IAC cone in the air passage to increase or decrease air bypassing the throttle valve to the intake manifold for control of idle speeds.

    The operation of all throttle bodies is basically the same. Each is constantly monitored by the computer control module in order to produce a 14.7:1 air/fuel ratio, which is vital to the catalytic converter operation.

    REMOVAL & INSTALLATION



    1. Release the fuel pressure. Refer to the fuel relief procedure in this section.
    2.  
    3. Disconnect the THERMAC hose from the engine fitting and remove the air cleaner.
    4.  
    5. Disengage the electrical connectors at the idle air control, throttle position sensor and the injector. Squeeze the plastic tabs on the injector connections and pull straight up.
    6.  

    See Figures 2 through 7



    Click image to see an enlarged view

    Fig. Fig. 2: Tag and disconnect the vacuum lines



    Click image to see an enlarged view

    Fig. Fig. 3: Tag and disengage the electrical connections



    Click image to see an enlarged view

    Fig. Fig. 4: Disconnect the linkages



    Click image to see an enlarged view

    Fig. Fig. 5: Use a flare nut wrench to disconnect the fuel lines

    1. Disconnect the grommet with wires from the throttle body.
    2.  
    3. Disconnect the throttle linkage, return spring, transmission control cable and cruise control (if equipped).
    4.  
    5. Disconnect the throttle body vacuum hoses, the fuel supply and fuel return lines.
    6.  
    7. Disconnect the bolts securing the throttle body, then remove it.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 6: Loosen and remove the bolts securing the throttle body



    Click image to see an enlarged view

    Fig. Fig. 7: Remove the throttle body from the intake manifold

    To install:
    1. Replace the manifold gaskets and O-rings.
    2.  
    3. Install the TBI unit and tighten the bolts to 12 ft. lbs. (16 Nm).
    4.  
    5. Install new O-rings into the fuel line nuts and then screw them on by hand. Tighten them to 20 ft. lbs. (26 Nm).
    6.  
    7. Connect the vacuum hoses and bracket.
    8.  
    9. Connect the throttle linkage, transmission control cable, return springs and cruise control cable.
    10.  
    11. Install the grommet (with harness connected) to the TBI.
    12.  
    13. Reconnect all electrical leads. Press the accelerator pedal to the floor and make sure that it releases properly.
    14.  
    15. Turn the ignition switch ON (but don't start the engine!) and check for leaks around the fuel line nuts.
    16.  
    17. Install the air cleaner and start the engine - check for leaks.
    18.  

    ADJUSTMENT



    See Figure 8

    Only if parts of the throttle body have been replaced should this procedure be performed; the engine should be at operating temperature.

    1. Remove the air cleaner, adapter and gaskets. Discard the gaskets. Plug any vacuum line ports, as necessary.
    2.  
    3. Leave the IAC valve connected and ground the diagnostic terminal (ALDL connector).
    4.  
    5. Turn the ignition switch to the ON position, do not start the engine. Wait for at least 30 seconds (this allows the IAC valve pintle to extend and seat in the throttle body).
    6.  
    7. With the ignition switch still in the ON position, disconnect the IAC electrical connector.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 8: Removing the idle stop screw

    1. Remove the ground from the diagnostic terminal and start the engine. Let the engine reach normal operating temperature.
    2.  
    3. Apply the parking brake and block the drive wheels. Remove the plug from the idle stop screw by piercing it first with a suitable tool, then applying leverage to the tool to lift the plug out.
    4.  
    5. Adjust the idle stop screw to the proper specifications
    6.  
    7. Turn the ignition OFF and reconnect the IAC valve connector. Unplug any plugged vacuum line ports and install the air cleaner, adapter and new gaskets.
    8.  

     
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