Toyota Pick-ups/Land Cruiser/4Runner 1970-1988

Mixture Control System (MC)

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OPERATION



See Figure 1

Carbureted Models Only

The mixture control system is used on carbureted models 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.

SERVICE



See Figures 2 and 3

  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.  



Click image to see an enlarged view

Fig. Fig. 1: Mixture control system component layout and vacuum diagram-1984-88 engines



Click image to see an enlarged view

Fig. Fig. 2: Checking the mixture control valve through 1980 year



Click image to see an enlarged view

Fig. Fig. 3: Checking the mixture control valve-1981-88 years

 
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