GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

Carbureted Engines

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Idle mixture and speed adjustments are critical aspects of exhaust emission control. It is important that all tune-up instructions be followed carefully to ensure satisfactory engine performance and minimum exhaust pollution. The different combinations of emission systems application on the various available engines have resulted in a great variety of tune-up specifications. All vehicles covered by this manual should have a decal conspicuously placed in the engine compartment giving tune-up specifications.

1.9L ENGINE



See Figures 1 and 2

In order to adjust the idle mixture you must first remove the plug that covers the mixture screw.

  1. Set the parking brake, block the drive wheels and place the transmission in Neutral.
  2.  
  3. Remove the carburetor from the engine, place it on a work bench and turn it upside down. For details, please refer to the carburetor procedures located in Chapter 4 of this manual.
  4.  
  5. Using a small prytool and a hammer, carefully drive the idle mixture screw metal plug from the base of the carburetor.
  6.  
  7. Reinstall the carburetor onto the engine. Start the engine and adjust the idle speed.
  8.  
  9. Allow the engine to reach normal operating temperatures, the choke must be Open and the A/C (if equipped) turned Off. Disconnect and plug the distributor vacuum line, the EGR vacuum line and the idle compensator vacuum lines.
  10.  



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Fig. Fig. 1: Removing the idle mixture screw plug-1.9L engine



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Fig. Fig. 2: Adjusting the idle speed-1.9L engine

  1. Turn the mixture screw all the way in, then back it out 1 1 / 2 turns.
  2.  

After adjustment, reconnect the vacuum lines.

  1. Adjust the throttle speed screw to 850 rpm (MT) or 950 rpm (AT).
  2.  
  3. Adjust the idle mixture screw to achieve the maximum speed.
  4.  
  5. Reset the throttle adjusting screw to 850 rpm (MT) or 950 rpm (AT).
  6.  
  7. Turn the idle mixture screw (clockwise) until the engine speed is reduced to 800 rpm (MT) or 900 rpm (AT).
  8.  
  9. If equipped with A/C, perform the following procedures:
    1. Turn the A/C to Max. Cold and the blower to High.
    2.  
    3. Open the throttle to 1 / 3 and allow it to close; this allows the speed-up solenoid to reach full travel.
    4.  
    5. Adjust the speed-up controller adjusting screw to set the idle to 900 rpm.
    6.  

  10.  

2.0L AND 2.8L ENGINES



The idle mixture adjustments are factory set and sealed; no adjustment attempt should be made, except by an authorized GM dealer.

Base Idle Adjustment
WITHOUT A/C

See Figures 3 and 4

  1. Refer to the emission control label on the vehicle and prepare the engine for adjustments.
  2.  
  3. Remove the air cleaner, set the parking brake and block the drive wheels.
  4.  
  5. Connect a tachometer to the distributor connector.
  6.  
  7. Place the transmission in Drive (AT) or Neutral (MT); make sure that the solenoid is energized.
  8.  
  9. Open the throttle slightly to allow the solenoid plunger to extend. Adjust the curb idle speed to the specified rpm by turning the solenoid screw.
  10.  
  11. De-energize the solenoid by disconnecting the electrical lead.
  12.  
  13. Set the base idle speed rpm by turning the idle speed screw. After adjustment, reconnect the solenoid electrical lead.
  14.  
  15. Remove the tachometer and install the air cleaner.
  16.  



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Fig. Fig. 3: Adjusting the idle speed on 2SE carburetors without A/C-2.0L and 2.8L engines



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Fig. Fig. 4: Adjusting the idle speed on the E2SE carburetors without A/C-2.0L and 2.8L engines

WITH A/C

See Figure 5

  1. Refer to the emission label on the vehicle and prepare the engine for adjustments.
  2.  
  3. Remove the air cleaner, set the parking brake and block the drive wheels.
  4.  
  5. Connect a tachometer to the distributor connector.
  6.  
  7. Place the transmission in Drive (AT) or Neutral (MT); make sure that the solenoid is energized.
  8.  
  9. Turn the A/C Off and set the curb idle speed by turning the idle speed screw.
  10.  
  11. Disconnect the A/C lead from the A/C compressor; make sure the solenoid is energized. Open the throttle slightly to allow the solenoid plunger to extend.
  12.  
  13. Turn the solenoid screw to adjust to the specified rpm. After adjustment, reconnect the A/C compressor lead, remove the tachometer and install the air cleaner.
  14.  



Click image to see an enlarged view

Fig. Fig. 5: Adjusting the idle speed on the E2SE carburetors with A/C-2.0L and 2.8L engines

Fast Idle Adjustment

See Figure 6

Following the adjustment of the base idle speed, the fast idle speed may be adjusted.

  1. Place the transmission in Park (AT) or Neutral (MT) and refer to the recommendation on the emission label.
  2.  
  3. Place the fast idle screw on the highest step of the fast idle cam.
  4.  
  5. Turn the fast idle screw to obtain the specified fast idle rpm.
  6.  



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Fig. Fig. 6: Fast idle speed adjustment-2.0L and 2.8L engines

 
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