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

Idle Mixture Adjustment

Print

PISTON ENGINES



All 1978-82 Models; 1983 GLC Wagon and 1986-87 Carbureted 323

Idle mixture adjustment for all 1978-82 Mazda piston engine cars, as well as 1983 GLC Wagons and 1986-87 carburetor-equipped 323s, requires the use of an HC/CO analyzer. Since this is an extremely expensive piece of equipment, the adjustment procedure is complex, and this adjustment is not required as a part of ordinary maintenance, no procedures are included here. This adjustment can, however, be checked at a reasonable cost at many diagnostic centers, or may be checked during mandatory vehicle emission inspections, where applicable. If the engine exhibits a rough idle and/or smoke, combined (in some cases) with hesitation or poor running at low speeds, the idle mixture might be at fault. First, check all the basic tune-up adjustments such as dwell, ignition timing, and spark plug condition, and verify that there are no vacuum leaks due to disconnected or leaking hoses. Then, if these symptoms persist, have the idle mixture checked with an HC/CO meter at a dealer or diagnostic center.

If incorrect readings are detected, we suggest you take the vehicle to a shop or dealer familiar with Mazdas and have the idle mixture adjusted according to the procedure specified by the factory.

1983-85 GLC (Except Wagon) and 626 (Except Diesel)

See Figures 1, 2 and 3

The carburetor must be removed and disassembled to gain access to the mixture screw since an idle mixture adjustment is normally only necessary in the event of carburetor overhaul. For information on carburetor removal and installation, please refer to Fuel System in this repair guide.

The air/fuel mixture for most 1983-85 carbureted piston engine models can readily be checked with a dwell/tachometer. An incorrect reading can indicate either an improper idle mixture or a faulty oxygen sensor. Make sure that the engine is properly tuned and that all vacuum hoses are properly connected before suspecting an improper idle mixture.

Do not secure the spring pin (which locks the mixture adjusting screw) until the adjustment has been performed.

To check/adjust the idle mixture:

  1. On 1984 626s only, disconnect and plug the idle compensator, thermosensor, and reed valve hoses.
  2.  
  3. Connect a tachometer to the engine.
  4.  
  5. Connect a dwell meter that can register up to 90 degrees (and which is suitable for four-cylinder engines). Connect the meter's positive (+/red) lead to terminal Y of the Air/Fuel (A/F) solenoid valve service connector, and the negative (-/black) lead to the engine.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: The mixture adjusting screw can be turned with a screwdriver



Click image to see an enlarged view

Fig. Fig. 2: A spring pin is used to lock the mixture adjusting screw in place



Click image to see an enlarged view

Fig. Fig. 3: Gently tap the spring pin into position after adjusting the idle mixture

  1. Warm up the engine to normal operating temperature and turn off all accessories.
  2.  
  3. Make sure the idle speed meets the following specifications; adjust it (if necessary), as described earlier in this section:

    1983-85 manual transaxle GLC: 850 rpm in Neutral
     
    1983-85 automatic transaxle GLC: 1,050 rpm in N (Neutral)
     
    1983-85 manual transaxle 626: 750 rpm in Neutral
     
    1983-85 automatic transaxle 626: 700 rpm in D (Drive)
     

  4.  

  1. With the engine running at the designated idle speed, note the reading on the dwell meter; the reading should be 32-40 degrees.
  2.  
  3. If the dwell reading is not within the appropriate range, adjust the idle mixture by turning the mixture adjusting screw, located near the base of the carburetor.
  4.  
  5. Make sure that the idle speed still meets specifications.
  6.  

Idle speed of the GLC with automatic transaxle should now be checked with the gear selector in D (Drive), but MAKE SURE the parking brake is set and the drive wheels are blocked. The correct reading is 750 rpm.

  1. After the mixture is properly set, press in the spring pin to lock the adjusting screw.
  2.  
  3. On 1984 626s only, unplug and reconnect the idle compensator, thermosensor, and reed valve hoses.
  4.  
  5. Disconnect the dwell meter and tachometer. Re-attach the A/F solenoid valve connector.
  6.  

1986-89 Fuel Injected Models

On all 1986-89 fuel injected piston engine vehicles covered by this information, idle mixture is automatically maintained by the electronic engine control unit, and thus, cannot be manually adjusted.

ROTARY ENGINES



Carbureted Vehicles

Most 1979-85 RX-7s were equipped with a carburetor.

Idle mixture adjustment is normally only necessary in the event of carburetor overhaul. For information on carburetor removal and installation, please refer to Fuel System in this repair guide.

  1. Remove the throttle body, then cut out the idle limiter cap with a hacksaw.
  2.  
  3. Assemble and install the carburetor. Be sure to install a new mixture adjusting screw. Tighten it lightly until it seats, then turn it counterclockwise three revolutions to attain the preliminary setting.
  4.  
  5. Connect a tachometer to the engine, then start the engine.
  6.  
  7. With the gear selector set to Neutral (or N), turn the throttle adjusting screw to adjust the idle speed to 770 rpm (manual transmission) or 870 rpm (automatic transmission). Read the tachometer as if testing a conventional 4-cylinder engine.
  8.  
  9. Set the idle speed to its highest rpm by turning the mixture adjusting screw, located at the base of the carburetor.
  10.  
  11. With the gear selector still set to Neutral (or N), again turn the throttle adjusting screw to adjust the idle speed to 770 rpm (manual transmission) or 870 rpm (automatic transmission).
  12.  
  13. Turn the mixture adjusting screw clockwise to lower the idle speed to 750 rpm (manual transmission) or 840 rpm (automatic transmission).
  14.  


CAUTION
When making adjustments with the engine running, especially with the automatic transmission in drive, ALWAYS make sure the parking brake is firmly set and the drive wheels are blocked in position.

  1. On vehicles equipped with an automatic transmission, shift the selector lever to the D position and adjust the idle speed to 750 rpm by turning the throttle adjusting screw.
  2.  
  3. Shut the engine OFF .
  4.  
  5. Install a new idle limiter cap onto the mixture adjustment screw.
  6.  

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 and remove the tachometer.
  2.  

Fuel Injected Vehicles
1984-85 RX-7

See Figures 4, 5, 6, 7 and 8

Idle mixture adjustment is normally only necessary when the variable resistor is replaced. The variable resistor should be replaced when it lacks continuity between terminals A and C or B and C, or whenever the engine is replaced.

  1. Switch all electrical accessories to the off position and remove the fuel filler cap.
  2.  
  3. Connect a tachometer to the engine.
  4.  



Click image to see an enlarged view

Fig. Fig. 4: Check the variable resistor for continuity between terminals A and C or B and C



Click image to see an enlarged view

Fig. Fig. 5: Use a pair of voltmeters or test lights to check the throttle sensor setting-1984-85 RX-7 with fuel injection



Click image to see an enlarged view

Fig. Fig. 6: If necessary, turn the throttle sensor adjusting screw-1984-85 RX-7 with fuel injection

  1. Start the engine and let it run until it reaches normal operating temperature.
  2.  
  3. Check/adjust the throttle sensor, as described in the idle speed adjustment procedure.
  4.  
  5. Disconnect the vent and vacuum solenoid valve connector.
  6.  
  7. Adjust the idle speed to 800 rpm by turning the Air Adjust Screw (AAS) on the throttle body.
  8.  
  9. Set the idle speed to its highest rpm by turning the adjusting screw on the variable resistor.
  10.  
  11. Once again, adjust the idle speed to 800 rpm by turning the Air Adjust Screw (AAS) on the throttle body.
  12.  



Click image to see an enlarged view

Fig. Fig. 7: Adjust idle speed by turning the AAS



Click image to see an enlarged view

Fig. Fig. 8: Adjust the variable resistor with a screwdriver

  1. Turn the variable resistor adjusting screw counterclockwise until the engine speed drops to 780 rpm, then turn it clockwise to reset the engine speed to 800 rpm.
  2.  
  3. Shut the engine OFF .
  4.  
  5. Disconnect and remove the tachometer.
  6.  
  7. Reattach the vent and vacuum solenoid valve connector.
  8.  
  9. Fill the head of the variable resistor adjusting screw with an adhesive agent (Part No. N304 23 795 or equivalent).
  10.  

1986-89 RX-7

See Figures 9, 10, 11, 12, 13, 14, 15, 16 and 17

Idle mixture adjustment is normally only necessary when the variable resistor is replaced. The variable resistor should be replaced if it lacks continuity between terminals A and C or B and C, or whenever the engine is replaced.



Click image to see an enlarged view

Fig. Fig. 9: Connect a jumper wire to the terminals of the initial set coupler-1986-89 RX-7



Click image to see an enlarged view

Fig. Fig. 10: Connect a tachometer to the service coupler at the trailing side coil with igniter-1986-89 RX-7



Click image to see an enlarged view

Fig. Fig. 11: Use dual checker lamps to verify the throttle sensor setting-1986-89 RX-7



Click image to see an enlarged view

Fig. Fig. 12: If necessary, turn the throttle sensor adjusting screw-1986-89 non-turbo RX-7



Click image to see an enlarged view

Fig. Fig. 13: If necessary, turn the throttle sensor adjusting screw-1986-89 turbocharged RX-7



Click image to see an enlarged view

Fig. Fig. 14: Adjust the idle speed by turning the AAS on the throttle body-1986-89 non-turbo RX-7



Click image to see an enlarged view

Fig. Fig. 15: On turbocharged RX-7 models, the AAS is located on the BAC valve

  1. Switch all electrical accessories to the off position.
  2.  
  3. Start the engine and let it run until it reaches normal operating temperature, then shut off the engine.
  4.  
  5. Connect a jumper wire to the terminals of the initial set coupler.
  6.  
  7. 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).
  8.  

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.

Click image to see an enlarged view

Fig. Fig. 16: Check the variable resistor for continuity between terminals A and C or B and C



Click image to see an enlarged view

Fig. Fig. 17: Adjust the variable resistor with a screwdriver

  1. Check/adjust the throttle sensor, as described in the idle speed adjustment procedure.
  2.  
  3. Remove the blind cap and adjust the idle speed to 750 rpm by turning the Air Adjust Screw (AAS) on the throttle body.
  4.  
  5. Set the idle speed to its highest rpm by turning the adjusting screw on the variable resistor.
  6.  
  7. Once again, adjust the idle speed to 750 rpm by turning the Air Adjust Screw (AAS) on the throttle body.
  8.  
  9. Turn the variable resistor adjusting screw counterclockwise until the engine speed drops to 730 rpm, then turn it clockwise to reset the engine speed to 750 rpm.
  10.  
  11. Shut off the engine and disconnect the tachometer.
  12.  
  13. Install the blind cap and disconnect the jumper wire.
  14.  

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

  1. Fill the head of the variable resistor adjusting screw with an adhesive agent (Part No. N304 23 795 or equivalent).
  2.  

 
label.common.footer.alt.autozoneLogo