Toyota Cressida and Van 1983-1990

Dashpot (DP) System



On fuel injected models, a dashpot system performs the same function as the throttle positioner that is used on a carbureted model. When decelerating, the dashpot opens the throttle valve slightly to lean out the temporarily rich fuel mixture and reduce the amount of HC and CO emissions. The system consists of the dashpot and a vacuum transducer valve with an air filter.


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Fig. Fig. 1 Adjusting the dashpot adjusting screw-Cressida

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Fig. Fig. 2 Adjust the dashpot as shown-Van

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Fig. Fig. 3 To test the vacuum transducer valve, blow air into either side and check for absence of air discharge

  1. Start the engine and warm it up so as to let the engine reach normal operating temperature.
  3. Check the idle speed and adjust as necessary.
  5. Maintain a engine speed of 3000 rpm.
  7. Pinch the vacuum hose between the dash pot and the vacuum transducer valve. (On the Van models, plug the hole in the back of the vacuum transducer valve).
  9. Release the throttle valve.
  11. Check the dashpot setting. The dash pot setting should be 2000 rpm.
  13. If not at specified speed, adjust the dashpot adjusting bolt or stopper screw.
  15. Inspect the vacuum transducer valve as follows:
    1. Set the dashpot speed in the same manner as described above.
    3. Release the pinched vacuum hose or the plugged hole (which ever the case may be) and check that the engine returns to idle speed in approximately 1 minute.
    5. If no problem is found in the inspection the system is in proper working order, otherwise inspect each component.

  17. Check the vacuum transducer valve by blowing air into each side.
  19. Check that the air flows without resistance from one side. The other side the air should flow without restriction.