Mazda Trucks 1987-1993 Repair Guide

Idle Speed and Mixture Adjustments

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IDLE SPEED



See Figure 1



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Fig. Fig. 1: Location of the idle speed adjusting screw-Pickup equipped with fuel injection

1987 Engines
EXCEPT B2200 W/AUTOMATIC TRANSMISSION
  1. Connect a tachometer to the engine.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Check the idle speed in NEUTRAL or PARK. If it is not 800-850 rpm, turn the Throttle Adjusting Screw until it is.
  6.  

B2200 W/AUTOMATIC TRANSMISSION AND WO/AIR CONDITIONING
  1. Connect a tachometer to the engine.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Disconnect the vacuum hose from the servo vacuum unit.
  6.  
  7. Connect direct intake vacuum to the servo vacuum unit.
  8.  
  9. Set the parking brake and block the wheels.
  10.  
  11. Check the idle speed in DRIVE. If it is not 920-970 rpm, turn the Throttle Adjusting Screw until it is.
  12.  
  13. Reconnect the hose properly.
  14.  

B2200 W/AUTOMATIC TRANSMISSION AND W/AIR CONDITIONING
  1. Connect a tachometer to the engine.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Disconnect the vacuum hose from the servo vacuum unit lower nipple.
  6.  
  7. Connect direct intake vacuum to the servo vacuum unit lower nipple.
  8.  
  9. Set the parking brake and block the wheels.
  10.  
  11. Check the idle speed in DRIVE. If it is not 1,300-1,500 rpm, turn the Throttle Adjusting Screw until it is.
  12.  
  13. Reconnect the hose properly.
  14.  

1988-93 CARBURETED ENGINES
  1. Connect a tachometer to the engine.
  2.  
  3. Run the engine to normal operating temperature, make sure the choke is fully opened. The cooling fan motor must not be operating during this operation.
  4.  
  5. Check the idle speed in NEUTRAL or PARK. If it is not 800-850 rpm, turn the Throttle Adjusting Screw until it is.
  6.  

1989-93 FUEL INJECTED ENGINES (EXCEPT NAVAJO)

See Figures 2 through 7



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Fig. Fig. 2: For idle speed adjustment, connect a jumper wire between the test connector green 1-pin and a good ground-Pickups equipped with fuel injection



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Fig. Fig. 3: Jumper wire attachment location-MPV equipped with the 2.6L engine



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Fig. Fig. 4: Location of the idle speed adjustment screw-MPV equipped with the 2.6L engine



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Fig. Fig. 5: Jumper wire attachment location-MPV equipped with the 3.0L engine



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Fig. Fig. 6: Location of the idle speed adjustment screw-MPV equipped with the 3.0L engine

  1. Place manual transmission in neutral or automatic transmission in park.
  2.  
  3. Make sure all accessories are Off.
  4.  
  5. Connect a tachometer and timing light to the engine.
  6.  
  7. Warm up the engine to normal operating temperature.
  8.  
  9. Check the ignition timing and adjust, if necessary.
  10.  
  11. Ground the green 1-pin test connector to the body with a jumper wire.
  12.  
  13. Check the idle speed. Specifications are as follows: 2.2L and 2.6L engines-Manual transmission: 730-770 rpm. Automatic transmission: 750-790 rpm. 3.0L engine-Manual and automatic transmission: 780-820 rpm.
  14.  
  15. If the idle speed is not within specification, adjust by turning the air adjusting screw.
  16.  
  17. After adjustment, disconnect the jumper wire from the test connector. Recheck the ignition timing.
  18.  

NAVAJO
  1. Place manual transmission in neutral or automatic transmission in Park. Apply the parking brake.
  2.  
  3. Make sure the heater and accessories are Off.
  4.  
  5. Start the engine and bring to normal operating temperature. Make sure the throttle lever is resting on the throttle plate stop screw.
  6.  
  7. Check the ignition timing and adjust, if necessary.
  8.  
  9. Shut off the engine and disconnect the negative battery cable for 5 minutes minimum.Reconnect the negative battery cable.
  10.  
  11. Start the engine and let it stabilize for 2 minutes. Rev the engine and let it return to idle, lightly depress and release the accelerator and let the engine idle.
  12.  
  13. If the engine does not idle properly, shut off the engine and disconnect the idle speed control-air bypass solenoid.
  14.  
  15. Run the engine at 2500 rpm for 30 seconds, then let it idle for 2 minutes.
  16.  
  17. Check/adjust the idle rpm to 675 rpm by turning the throttle plate stop screw.
  18.  

If the screw must be turned in, shut the engine off and make the estimated adjustment, then start the engine and repeat Steps 8 and 9.

  1. Shut the engine off and repeat Steps 8 and 9.
  2.  
  3. Shut the engine off and disconnect the negative battery cable for 5 minutes minimum.
  4.  
  5. With the engine off, reconnect the idle speed control-air bypass solenoid. Make sure the throttle is not stuck in the bore and the linkage is not preventing the throttle from closing.
  6.  
  7. Start the engine and let it stabilize for 2 minutes. Rev the engine and let it return to idle, lightly depress and release the accelerator and let the engine idle.
  8.  

A condition may occur where the engine rpm will oscillate. This can be caused by the throttle plates being open enough to allow purge flow. To make sure of this condition, disconnect the carbon canister purge line and plug it. If purge is present, the throttle plates must be closed until the purge flow induced idle oscillations stop.

MIXTURE ADJUSTMENT



1987-88 Engines

You'll need a dwell meter with a 90° scale.

  1. Run the engine to normal operating temperature.
  2.  
  3. On the 2.6L engine, connect the dwell meter (+) positive lead to the yellow/green wire in the check connector, located near the No.3 air control valve and reed valve case assembly. Connect the (-) lead to ground.
  4.  
  5. On the 2.2L engine, connect the dwell meter (+) positive lead to the brown/yellow wire in the check connector, located near the No.3 air control valve and reed valve case assembly. Connect the (-) lead to ground.
  6.  
  7. With the engine at the normal idle speed, the dwell meter should read 27-45° for the 2.6L engine, or 20-70° for the 2.2L engine.
  8.  
  9. If not, check the oxygen sensor, the wiring between the oxygen sensor and the feedback control unit, and the control unit itself. See Fuel System for procedures. If all components check out satisfactorily, adjust the mixture with the adjusting screw.
  10.  

1989-93 Engines

The idle mixture is controlled by the Electronic Control Unit (ECU) and is not adjustable.

See Figure 7



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Fig. Fig. 7: Gasoline Engine Tune-Up Specification

 
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