Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Idle Speed Adjustment

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PISTON ENGINES



1978-87 Models
EXCEPT 626 DIESEL

See Figures 1, 2 and 3

Idle speed adjustments are easily accomplished, but you must be careful to perform them under the proper conditions. The engine must be fully warmed up. The best procedure is to drive the vehicle for several miles after the temperature gauge indicates that the coolant has reached operating temperature. All normal operating conditions should be maintained. For example, the air cleaner and all vacuum hoses should be installed or connected, the choke should be wide open, and all accessories should be off. This includes the engine cooling fan if it is electrical. If necessary, unplug it. Also, avoid extremes of outside temperature, and replace a thermostat that makes the engine operate too hot or too cold before proceeding.



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Fig. Fig. 1: Disconnect the air bypass solenoid connector when checking idle speed on a 1987 626 below sea level



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Fig. Fig. 2: Adjusting the idle speed on carbureted 323s-Carbureted GLC and 626 models similar



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Fig. Fig. 3: Adjusting the idle speed on fuel injected 323 models-626 fuel injected models similar

On the 1978-79 GLC and 1979 626 models, disconnect the canister purge hose between the canister and the air cleaner. On the 1986-87 626 and MX-6, run the engine at 2,500-3,000 rpm in Neutral for three minutes before proceeding.

  1. Warm up the engine to normal operating temperature and turn off all accessories.
  2.  
  3. Connect a reliable tachometer according to tool manufacturer's instructions (usually between the coil negative (-) terminal and ground).
  4.  
  5. On 1987 626s only, disconnect the air bypass solenoid connector at altitudes of less than 3,280 feet or 1,000 meters (sea level).
  6.  
  7. Note the idle speed. Compare this reading to the appropriate range in the Tune-Up Specifications chart located in this section.
  8.  

Read the tachometer's 4-cylinder scale, for both rotary and piston engines. If the tachometer has only a 6-cylinder scale and an 8-cylinder scale, read the 8-cylinder scale and multiply all readings by two to get the correct rpm. For example, if the specified rpm is 700, set the idle speed at 350 rpm, as indicated on the 8-cylinder scale.

  1. If the idle speed does not fall within the designated range, locate and turn the appropriate idle speed adjusting screw until the desired reading is attained:
    1. On carburetor-equipped engines, the throttle adjusting screw is usually located on the lower portion of the carburetor near the throttle valve shaft. The screw acts directly on a flange which is integral with the throttle shaft; it does not actuate any cams or levers.
    2.  
    3. On models equipped with electronic fuel injection, the air adjusting screw is located on top of the throttle body.
    4.  

  2.  
  3. On 1986-87 323s, after adjusting the idle speed, the dashpot must be adjusted as follows:
    1. Start the engine and warm it up to normal operating temperature.
    2.  
    3. With the tachometer still connected, increase the engine speed to 3,000 rpm, then slowly reduce the engine speed and make sure the dashpot rod contacts the lever at 2,400-2,600 rpm.
    4.  
    5. If it does not operate as described, loosen the locknut and adjust the rod by turning the dashpot.
    6.  

  4.  
  5. On 1987 626s, fasten the air bypass solenoid connector, if applicable.
  6.  
  7. Disconnect and remove the tachometer.
  8.  

626 DIESEL ENGINE

See Figures 4 and 5

Adjusting the idle speed on the diesel requires you to have a special tachometer which measures idle speed from a special sensor on the injection pump.

  1. Turn all of the vehicle's accessories to the off position, then connect a diesel tachometer, according to the tool manufacturer's instructions.
  2.  



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Fig. Fig. 4: Checking and adjusting accelerator cable deflection on the 626 diesel



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Fig. Fig. 5: Adjust idle speed on the 626 diesel by (1) loosening the locknut, then (2) turning the adjusting bolt

  1. Place a ruler near the accelerator pedal and then depress the pedal to determine the play in the cable. It should be 0.04-0.12 in. (1-3mm). If necessary, lengthen the cable (to increase play) by loosening the nut on the firewall side of the cable bracket and then tightening the nut on the other side. You would shorten the cable, in order to decrease play, by reversing the order in which the nuts are loosened.
  2.  
  3. Drive the car until several miles after the temperature gauge indicates normal operating temperature, to warm up the engine. Measure the engine rpm with the tachometer.
  4.  
  5. If the rpm is outside the range of 800-850 rpm, loosen the locknut on the idle adjusting bolt on the injection pump. Then, turn the bolt clockwise to increase the idle speed or counterclockwise to decrease it. Secure the adjusting bolt with the locknut.
  6.  
  7. Disconnect and remove the tachometer.
  8.  

1988-89 Models

See Figures 6 and 7

The idle speed is controlled automatically by the Idle Speed Control (ISC) solenoid valve, and adjustment is usually not necessary. However, if rough idling occurs when pin 1 of the green test connector is grounded, then adjustment of the idle speed is required. If adjustment is necessary, proceed as follows:

  1. Turn all of the vehicle's accessories to the off position, then connect a tachometer to the engine check connector (see illustration).
  2.  



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Fig. Fig. 6: Tachometer hooked up to the underhood check connector-929 shown



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Fig. Fig. 7: Idle speed adjustment for the 929-other models similar

  1. Warm up the engine to normal operating temperature.
  2.  
  3. Ground pin 1 of the green test connector with a jumper wire. (An illustration of this step is shown in the ignition timing portion of this section.)
  4.  
  5. With the test connector grounded, check the idle speed. Compare this reading to the Tune-Up Specifications chart located in this section. If it is not within the specified range, remove the rubber cap from the air adjusting screw on the throttle body and turn the screw to adjust the idle speed.
  6.  
  7. Once the idle speed is within specification, install the cap and disconnect the jumper wire from the test connector.
  8.  
  9. On 1988 323s, after adjusting the idle speed, the dashpot must be adjusted as follows:
    1. Start the engine and warm it up to normal operating temperature.
    2.  
    3. With the tachometer still connected, increase the engine speed to 3,000 rpm, then slowly reduce the engine speed and make sure the dashpot rod contacts the lever at 2,400-2,600 rpm.
    4.  
    5. If it does not operate as described, loosen the locknut and adjust the rod by turning the dashpot.
    6.  

  10.  
  11. Disconnect and remove the tachometer.
  12.  

ROTARY ENGINES



Carbureted Vehicles

All 1979-83 RX-7s were equipped with a carburetor. 1984-85 RX-7s were equipped with either a carburetor (12A engine) or fuel injection (13B engine).

  1. If possible, set up an extra cooling fan to blow additional air into the engine compartment.
  2.  
  3. Set the parking brake and block the wheels.
  4.  
  5. Switch all accessories to the off position.
  6.  
  7. Remove the fuel tank filler cap.
  8.  
  9. On 1979-83 models, disconnect and plug the hose at the idle compensator in the air cleaner. On 1984-85 vehicles with a manual transmission, disconnect the richer solenoid connector.
  10.  

On 1981-83 models, make sure the throttle opener (if equipped with air conditioning) and dashpot do not prevent the idle lever from returning to the idle stop.

  1. Connect a tachometer to the engine.
  2.  
  3. Start the engine and allow it to reach normal operating temperature. On vehicles equipped with an automatic transmission, shift the selector lever to the D (Drive) position.
  4.  
  5. Check the idle speed with the tachometer. (Read the tachometer as if testing a conventional 4-cylinder engine.) If the idle speed is not correct, adjust it by turning the throttle adjusting screw on the carburetor.
  6.  

Read the tachometer's 4-cylinder scale, for both rotary and piston engines. If the tachometer has only a 6-cylinder scale and an 8-cylinder scale, read the 8-cylinder scale and multiply all readings by two to get the correct rpm. For example, if the specified rpm is 700, set the idle speed at 350 rpm, as indicated on the 8-cylinder scale.

  1. Unplug and reconnect the hose at the idle compensator on the air cleaner, or secure the richer solenoid connector, if applicable. Install the fuel tank filler cap.
  2.  

After adjusting idle speed, the throttle sensor on the carburetor should also be adjusted. For information on that procedure, please refer to Fuel System in this repair guide.

  1. Disconnect the tachometer and unblock the wheels.
  2.  

Fuel Injected Vehicles
1984-85 RX-7

See Figures 8, 9 and 10

  1. Switch all electrical accessories to the off position and remove the fuel filler cap.
  2.  
  3. Start the engine and let it run until it reaches normal operating temperature.
  4.  



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Fig. Fig. 8: Use a pair of voltmeters or test lights to check the throttle sensor setting-1984-85 fuel injected RX-7



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Fig. Fig. 9: If necessary, turn the throttle sensor adjusting screw-1984-85 fuel injected RX-7



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Fig. Fig. 10: Adjust idle speed by turning the AAS

  1. Check/adjust the throttle sensor by performing the following:
    1. With the engine OFF , connect a pair of voltmeters to the green check connector as shown in the illustration. If voltmeters are not available, a dual set of test lights may be used instead.
    2.  
    3. Turn the ignition switch ON and check to see if current flows to one of the voltmeters. When using the test light method, the light will illuminate when current flows.
    4.  
    5. If there is no current, remove the rubber cap from the throttle sensor screw and turn the screw clockwise only until current flow is indicated on one of the voltmeters (or test lights). If both voltmeters show current, remove the cap and turn the screw counterclockwise so that current flows to only one voltmeter (or test light).
    6.  
    7. Install the rubber cap and disconnect the voltmeters.
    8.  

  2.  
  3. Once the throttle sensor is adjusted, disconnect the vent and vacuum solenoid connector.
  4.  
  5. Connect a tachometer, then start the engine.
  6.  
  7. Adjust the idle speed to 800 rpm by turning the Air Adjust Screw (AAS) on the throttle body. After adjusting the idle speed, reinstall the blind cap onto the AAS, if so equipped.
  8.  
  9. Shut off the engine, then attach the vent and vacuum solenoid connector. Disconnect and remove the tachometer, then install the fuel tank filler cap.
  10.  

1986-89 RX-7

See Figures 11, 12, 13, 14, 15, 16 and 17

  1. Switch off all electrical accessories. Start the engine and let it run until it reaches normal operating temperature, then shut off the engine.
  2.  
  3. Connect a jumper wire to the terminals of the initial set coupler.
  4.  
  5. Connect a tachometer to the service coupler at the trailing side coil with igniter. If the tachometer does not function correctly, reconnect it at the leading side coil with igniter (black coupler).
  6.  

If using an inductive (secondary pick-up) type tachometer, connect it only at the trailing side of the spark plug wires. If connected at the leading side coil with igniter, it will not function properly.

  1. Check/adjust the throttle sensor by performing the following:
    1. With the engine OFF , connect dual checker lamps 49 F018 001 or equivalent to the green check connector.
    2.  
    3. Turn the ignition switch to the ON position and check that one of the lamps illuminates.
    4.  
    5. If both lamps illuminate or neither one does, turn the throttle sensor adjusting screw until only one of the lamps illuminates. If both of the lamps illuminate, remove the rubber cap and turn the screw counterclockwise. If neither lamp illuminates, turn the screw clockwise. Do not use excessive pressure on the screw.
    6.  
    7. Remove the checker lamps and reinstall the rubber cap.
    8.  

  2.  
  3. On 1986-89 non-turbo models, remove the blind cap from the throttle body and adjust the idle speed by turning the Air Adjust Screw (AAS). On 1987-89 turbocharged models, remove the blind cap from the Bypass Air Control (BAC) valve and adjust the idle speed by turning the AAS.
  4.  
  5. When adjustment is complete, shut the engine OFF , then disconnect and remove the tachometer.
  6.  



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Fig. Fig. 11: Connect a jumper wire to the terminals of the initial set coupler-1986-89 RX-7



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Fig. Fig. 12: Connect a tachometer to the service coupler at the trailing side coil with igniter-1986-89 RX-7



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Fig. Fig. 13: Use dual checker lamps to verify the throttle sensor setting-1986-89 RX-7



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Fig. Fig. 14: If necessary, turn the throttle sensor adjusting screw-1986-89 non-turbo RX-7



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Fig. Fig. 15: If necessary, turn the throttle sensor adjusting screw-1986-89 turbocharged RX-7



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Fig. Fig. 16: Adjust the idle speed by turning the AAS on the throttle body-1986-89 non-turbo RX-7



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Fig. Fig. 17: On turbocharged RX-7 models, the AAS is located on the BAC valve

  1. Install the blind cap and disconnect the jumper wire from the initial set coupler.
  2.  

Be sure to remove the jumper wire, otherwise engine performance will be reduced.

 
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