SYSTEM OPERATION

See Figure 1

The operation of this system reduces the HC and CO emissions. When decelerating, the dash pot opens the throttle valve slightly more than at idle. This causes the air-fuel mixture to burn completely.



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Fig. Fig. 1: The dash pot actuates the throttle lever-4A-GE engine shown

ADJUSTMENT

4A-GE Engine

See Figure 2

  1. Warm up and stop engine.
    2.  
  2. Check idle speed.
    3.  



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Fig. Fig. 2: Exploded view of the Vacuum Thermal Valve (VTV) assembly

  1. Disconnect the throttle cables from the throttle cam.
    2.  
  2. Remove the VTV cap, filter and separator from the dash pot.
    3.  
  3. Adjust DP setting speed as follows:
    1. Race the engine at 2500 rpm for a few seconds. Plug the VTV hole with your finger in the dash pot assembly.
      2.  
    2. Release the throttle valve.
      3.  
    3. Check the DP setting speed. The DP setting speed is 1800 rpm with cooling fan OFF.
      4.  
    4. Adjust the DP setting speed by turning the DP adjusting screw.
      5.  

    4.  
  4. Reinstall the DP separator, filter and VTV cap.
    5.  
  5. Connect the throttle cables to the throttle cam.
    6.  
  6. Check system operation by racing the engine at 2500 rpm for a few seconds, release the throttle valve and check that the engine returns to idle speed in a few seconds.
    7.  

4A-FE Engine

The 1993-97 4A-FE engines do not use this system.

  1. Warm up and stop engine.
    2.  
  2. Check idle speed and adjust, if necessary.
    3.  
  3. Remove the cap, filter and separator from the dash pot.
    4.  
  4. Adjust DP setting speed as follows:
    1. Connect terminals TE1 and E1 in the check connector.
      2.  
    2. On 2WD California and 4WD, disconnect the EGR VSV connector.
      3.  
    3. Race the engine at 3000 rpm (2WD) or 3500 rpm (4WD) for a few seconds. Plug the VTV hole with your finger in the dash pot assembly.
      4.  
    4. Release the throttle valve.
      5.  
    5. Check the DP setting speed. The DP setting speed should be 1500 rpm on 2WD, 1800 rpm on 4WD with M/T or 2200 rpm on 4WD with A/T, with cooling fan OFF.
      6.  
    6. Adjust the DP setting speed by turning the DP adjusting screw.
      7.  
    7. Connect the EGR VSV connector if so equipped. Remove the SST or jumper from the check connector.
      8.  

    5.  
  5. Reinstall the DP separator, filter and cap.
    6.  
  6. Check system operation by racing the engine at 3000 rpm (2WD) or 3500 rpm (4WD) for a few seconds, release the throttle valve and check that the engine returns to idle speed in a few seconds.
    7.  

REMOVAL & INSTALLATION

  1. To remove the dash pot assembly, unplug the vacuum hose then remove the dash pot mounting screws.
    2.  
  2. Remove the assembly from the throttle body.
    3.  
  3. Installation is the reverse of removal. Replace the dash pot assembly and adjust if necessary.
    4.