Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Idle Speed Control (ISC) valve

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OPERATION



To improve idle smoothness, the ISC system controls the intake air amount by regulating the bypass air amount that passes through the throttle body. By regulating this air amount, the computer has the ability to increase or decrease the engine idle speed.

TESTING



See Figures 1, 2 and 3

  1. Detach the ISC valve connector when the engine is cold and idling.
  2.  
  3. Note the engine rpm and reconnect the connector.
  4.  
  5. Warm the engine to normal operating temperature and detach the connector again.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: To test the ISC valve, disconnect the IAC valve electrical plug



Click image to see an enlarged view

Fig. Fig. 2: Measure the resistance across both terminals of the ISC valve, at the temperature specified in the text for each model

  1. Verify the engine rpm is lower with the ISC detached when the engine is warm.
  2.  
  3. Check the resistance of the valve using an ohmmeter.
  4.  
  5. The resistance should be approximately:

    1990-92 626 and MX-6: 6.3-9.9 ohms at normal operating temperature.
     
    1993-98 626/MX-6/Probe: 7.7-9.3 ohms at 73°F (23°C).
     
    1990-94 323 and Protege: 11-13 ohms at 68°F (20°C).
     
    1995-98 Protege: 7.7-9.3 ohms at 73°F (23°C).
     
    MX-3 and Millenia: 10.7-12.3 ohms at 68°F (20°C).
     

  6.  
  7. If not as specified, remove the valve from the throttle body.
  8.  
  9. Blow air through the valve port A and verify that no air comes out of port B when the valve is at normal operating temperature.
  10.  



Click image to see an enlarged view

Fig. Fig. 3: With the valve removed, cool it down at point A and watch the valve movement at B

  1. Allow the valve to cool. Watch the movement of the valve as it cools, it should open.
  2.  
  3. Blow air through the valve port A and verify air comes out of port B when the valve is cold.
  4.  
  5. If not as specified, replace the valve.
  6.  

REMOVAL & INSTALLATION



See Figure 4

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary for access, remove the air intake piping to the throttle body.
  4.  
  5. Detach the electrical harness connection from the valve, or valve pigtail.
  6.  



Click image to see an enlarged view

Fig. Fig. 4: Exploded view of the ISC valve (throttle body mounted)

  1. Disconnect any hoses from the ISC valve. Some valves will also have engine coolant hoses connected to them. Plug the engine coolant hoses to minimize coolant leakage.
  2.  
  3. Remove the ISC valve attaching bolts.
  4.  
  5. Remove the ISC valve from the throttle body or intake manifold.
  6.  
  7. Thoroughly clean the gasket mating surfaces.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

 
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