Mazda Trucks 1987-1993 Repair Guide

Idle Air Control (IAC) Valve

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OPERATION



See Figure 1

The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows air, determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.



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Fig. Fig. 1: Typical Idle Air Control (IAC) valve which is mounted to the throttle body-cutaway view shows air bypass direction

TESTING



Navajo Models

See Figure 2

  1. Turn the ignition switch to the OFF position.
  2.  
  3. Disengage the wiring harness connector from the IAC valve .
  4.  
  5. Using an ohmmeter, measure the resistance between the terminals of the valve.
  6.  

Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR terminal and the negative lead on the ISC terminal.

  1. If the resistance is not 7-13 ohms, replace the IAC valve.
  2.  



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Fig. Fig. 2: IAC valve wiring harness connections

Pick-up and MPV Models

See Figure 3

The Idle Air Control (IAC) valve is an integral component of the Bypass Air Control (BAC) valve.

  1. Turn the ignition switch to the OFF position.
  2.  
  3. Disengage the wiring harness connector from the IAC valve .
  4.  
  5. Using an ohmmeter, measure the resistance between the terminals of the valve.
  6.  



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Fig. Fig. 3: Checking the resistance of the IAC valve on the BAC valve assembly

  1. The resistance should measure 10.7-12.3 ohms at 68° F (20° C) for 3.0L equipped models and 7.7-9.3 ohms at 73° F (23° C) for 2.6L engine equipped models.
  2.  
  3. If the resistance does not measure within specifications, replace the BAC valve.
  4.  

REMOVAL & INSTALLATION



Navajo Models

See Figures 4, 5, 6 and 7

  1. Disconnect the negative battery cable.
  2.  



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Fig. Fig. 4: To remove the IAC valve, first disconnect the negative battery cable, then the IAC wire harness plug



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Fig. Fig. 5: Next, remove the two IAC valve attaching bolts ...



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Fig. Fig. 6: ... and pull the valve from the intake manifold

  1. Disengage the wiring harness connector from the IAC valve.
  2.  
  3. Remove the two retaining screws, then remove the IAC valve and discard the old gasket.
  4.  

To install:


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Fig. Fig. 7: When installing the valve, always discard the old gasket and install it using a new one

  1. Clean the IAC valve mounting surface on the throttle body of old gasket material.
  2.  
  3. Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71-106 inch lbs. (8-12 Nm).
  4.  
  5. Attach the wiring harness connector to the IAC valve.
  6.  
  7. Connect the negative battery cable.
  8.  

Pick-up and MPV Models

See Figure 8

The Idle Air Control (IAC) valve is an integral component of the Bypass Air Control (BAC) valve.

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the water hoses (if equipped) and air hose from the BAC/IAC valve.
  4.  



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Fig. Fig. 8: Removal of the BAC/IAC valve assembly-3.0L engine shown

  1. Disengage the wiring harness connector from the BAC/IAC valve.
  2.  
  3. Remove the mounting fasteners from the valve assembly.
  4.  
  5. Remove the BAC/IAC valve assembly, along with the mounting gasket and O-ring from the vehicle.
  6.  

To install:
  1. Remove any foreign material from the contact surface.
  2.  
  3. Install the BAC/IAC valve assembly, with a new mounting gasket and O-ring, onto the engine in correct position.
  4.  
  5. Install and tighten the mounting fasteners to 14-18 ft. lbs. (19-25 Nm) on 3.0L engines, and 22-30 inch lbs. (2.5-3.4 Nm) on 2.6L engines.
  6.  
  7. Plug in the valve wiring harness connector.
  8.  
  9. Connect the air hose and water hoses (if equipped) to the valve assembly.
  10.  
  11. Connect the negative battery cable.
  12.  
  13. If equipped with water hoses, verify that the valve assembly does not leak.
  14.  

 
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