Toyota Celica/Supra 1971-1985 Repair Guide

Mixture Control (MC) System

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See Figures 1, 2 and 3

The mixture control system is used on 1980-82 model Celicas with manual transmissions in order to reduce HC and CO emissions under sudden deceleration. When the throttle is suddenly closed, the vacuum created opens the valve and allows fresh air to pass into the intake manifold.



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Fig. Fig. 1: Location of the mixture control valve-22R engines shown



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Fig. Fig. 2: Schematic of the mixture control system operation



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Fig. Fig. 3: Mixture control system operating conditions

TESTING



See Figures 4 and 5



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Fig. Fig. 4: Disconnect the vacuum hose from the MC valve; no suction should be felt at the air inlet



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Fig. Fig. 5: Reconnect the hose and check that the vacuum is felt momentarily

  1. Start the engine.
  2.  
  3. Disconnect the vacuum sensing hose (top) from the MC valve.
  4.  
  5. Place your hand over the air inlet of the valve and check that no suction can be felt.
  6.  
  7. Reconnect the vacuum sensing hose. Suction should be felt momentarily.
  8.  

At this time the engine will idle roughly or stall out altogether. This is normal.

  1. If the valve is not operating properly is will require replacement.
  2.  

 
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