GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Throttle Body

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REMOVAL & INSTALLATION



See Figures 1 and 2

  1. Properly relieve fuel system pressure, then disconnect the negative battery cable.
  2.  
  3. Disconnect the THERMAC hose from the engine fitting and remove the air cleaner assembly.
  4.  
  5. Tag and disengage the electrical connectors from the idle air control valve, throttle position sensor and the fuel injectors.
  6.  
  7. Disconnect the throttle linkage, return spring(s) and Cruise Control (if equipped).
  8.  
  9. Tag and disconnect the throttle body vacuum hoses, the fuel supply and fuel return lines.
  10.  
  11. Loosen and remove the fasteners securing the throttle body to the intake manifold, then remove it and the gasket.
  12.  
  13. If the throttle body is to remain off the engine for any length of time, cover the opening in the intake manifold to keep debris out of the engine.
  14.  

To install:
  1. Thoroughly clean the gasket mating surfaces of any remaining gasket material.
  2.  
  3. Install the throttle body to the intake manifold using a new gasket, then install the retainers and tighten to 11 ft. lbs. (15 Nm).
  4.  
  5. Connect the fuel supply and return lines to the throttle body using new O-rings.
  6.  
  7. Connect the throttle body vacuum hoses as noted during removal, then connect the throttle linkage and return spring(s). If equipped, connect the Cruise Control.
  8.  
  9. Engage the electrical connectors to the idle air control valve, TPS and injectors, as noted during removal.
  10.  
  11. Install the air cleaner and connect the THERMAC hose.
  12.  
  13. Connect the negative battery cable, then start the engine and check for leaks.
  14.  



Click image to see an enlarged view

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



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Fig. Fig. 2: Removing the TBI unit from the intake manifold

INJECTOR REPLACEMENT



See Figures 3, 4 and 5


WARNING
When removing the injectors, be careful not to damage the electrical connector pins (on top of the injector), the injector fuel filter and the nozzle. The fuel injector is serviced as a complete assembly ONLY. The injector is an electrical component and should not be immersed in any kind of cleaner.

  1. Disconnect the negative battery cable and properly relieve the fuel system pressure.
  2.  
  3. Remove the air cleaner assembly from the engine.
  4.  
  5. At the injector connector, squeeze the two tabs together and pull straight up to disengage the connector from the injector.
  6.  


CAUTION
Do not remove the screws retaining the pressure regulator to the fuel meter cover. The regulator includes a large spring under heavy compression which, if accidentally released, could cause personal injury.

  1. Loosen the screws, then remove the screws and lockwashers securing the fuel meter cover. Remove the cover from the fuel meter body, but leave the cover gasket in place.
  2.  
  3. Using a small pry bar and a round fulcrum, or tool No. J-26868, carefully pry or lift the injector until it is free of the fuel meter body.
  4.  
  5. Remove the small O-ring from the nozzle end of the injector. Carefully rotate the injector's fuel filter back and forth to remove it from the base of the injector.
  6.  
  7. Remove and discard the fuel meter cover gasket.
  8.  
  9. Remove the large O-ring and back-up washer from the top of the counterbore of the fuel meter body injector cavity.
  10.  

To install:
  1. With the larger end of the filter facing the injector (so that the filter covers the raised rib of the injector base) install the filter by twisting it into position on the injector.
  2.  
  3. Lubricate the new O-rings with clean automatic transmission fluid, then install the small O-ring on the nozzle end of the injector. Be sure the O-ring is pressed up against the injector fuel filter.
  4.  
  5. Install the steel backup washer in the top counterbore of the fuel meter body's injector cavity, then install the new large O-ring directly over the backup washer. Make sure the O-ring is properly seated in the cavity and is flush with the top of the fuel meter body casting surface.
  6.  

If the backup washer and large O-ring are not properly installed BEFORE the fuel injector, a fuel leak will likely result.

  1. Install the fuel injector into the cavity by aligning the raised lug on the injector base with the cast notch in the fuel meter body cavity. Once the injector is aligned, carefully push down on the injector by hand until it is fully seated in the cavity. When properly aligned and installed, the injector terminals will be approximately parallel to the throttle shaft.
  2.  
  3. Install a new dust seal into the recess on the fuel meter body and a new fuel outlet gasket on the fuel meter cover.
  4.  
  5. Position a new cover-to-body gasket, then install the fuel meter cover to the body making sure all new gaskets are properly in position.
  6.  
  7. Coat the threads of the cover retaining screws with a threadlocking compound such as Loctite® 262, or equivalent. Install the screws and lockwashers, then carefully tighten to 28 inch lbs. (3 Nm).
  8.  

Do not use a stronger threadlocking compound or screw removal may be excessively difficult. If the improper compound is used, the screw heads could break off when attempting to loosen them at some future time.

  1. Engage the injector electrical connector, then install the air cleaner assembly.
  2.  
  3. Connect the negative battery cable, then start the engine and check for leaks.
  4.  



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Fig. Fig. 3: Exploded view of the fuel meter cover



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Fig. Fig. 4: The injector may be removed by carefully prying upward using a small prytool and a round fulcrum



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Fig. Fig. 5: Exploded view of the fuel injector and O-ring seal installation

IDLE AIR CONTROL (IAC) VALVE REPLACEMENT



See Figures 6, 7 and 8

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly from the engine.
  4.  
  5. Disengage the electrical connector from the idle air control valve.
  6.  
  7. Using a 1 1 / 4 (32mm) wrench or tool J-33031, loosen and remove the idle air control valve from the throttle body assembly.
  8.  

To install:

WARNING
Before installing a new idle air control valve, measure the distance that the valve extends (from the motor housing to the end of the cone); the distance should be no greater than11/8in. (28mm). If it is extended too far, damage will occur to the valve when it is installed.

  1. Measure the valve pintle extension. If it is excessive, identify the valve as a type-I or type-II. The type I valve has a collar at the electric terminal end while the type-II does not. To retract the valve pintle on a type-I valve, use firm thumb pressure and, if necessary, rock the pintle with a slight side-to-side motion. For type-II valves, compress the retaining spring by hand and turn the valve inward using a clockwise motion. Once the pintle is retracted for type-II valves, make sure the straight portion of the spring is again aligned with the flat on the valve.
  2.  
  3. Install the valve to the throttle body using a new gasket, then carefully tighten the valve to 13 ft. lbs. (18 Nm).
  4.  
  5. Engage the valve electrical connector, then install the air cleaner assembly.
  6.  
  7. Connect the negative battery cable, then start and run the engine until it reaches normal operating temperature.
  8.  
  9. Shut the engine OFF and the ECM will reset the IAC valve pintle.
  10.  



Click image to see an enlarged view

Fig. Fig. 6: Identification and installation of the IAC valve



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Fig. Fig. 7: Retracting the IAC valve pintle on type-I valves (with collar at terminal end)



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Fig. Fig. 8: Retracting the IAC valve pintle on type-II valves (without collar)

THROTTLE POSITION SENSOR (TPS) SERVICE



The throttle position sensor used on the fuel injected engine is non-adjustable. If sensor problems are suspected, test sensor output using a scan tool or voltmeter. The sensor must be replaced if defective.

Testing
  1. If available, connect a scan tool to the ECM test connector. If a scan tool is not available, use a voltmeter to backprobe the TPS connector terminals A (black wire on end of connector) and B (dark blue wire at center of connector). By backprobing the connector a voltage reading can be taken without disconnecting the circuit and without piercing the wires.
  2.  
  3. Turn the ignition ON , but do not start the engine. Check the voltmeter or scan tool for TPS output. Voltage should be 1.25 volts or less with the throttle closed. Voltage may go as high as 4.5 volts at wide open throttle.
  4.  
  5. If voltage with the throttle closed is greater than 1.25 volts, replace the switch.
  6.  

Replacement

The throttle position sensor is an electrical component. Do NOT soak it or clean it with solvent or the sensor could be damaged.

  1. Disconnect the negative battery cable, then remove the air cleaner assembly for access.
  2.  
  3. Disengage the TPS electrical connector.
  4.  
  5. Loosen the TPS attaching screws, then remove the sensor from the throttle body.
  6.  

To install:
  1. Install the TPS to the throttle body assembly while aligning the TPS lever with the drive lever on the throttle body.
  2.  
  3. Install the retaining screws and tighten to 18 inch lbs. (2.0 Nm).
  4.  
  5. Engage the sensor connector, then install the air cleaner assembly.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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