GM Cadillac 1967-1989 Repair Guide

Fuel Injected Engines

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Idle speed adjustment is not required unless throttle body parts have been replaced, the Throttle Position Sensor (TPS) and/or the Idle Speed Control (ISC) have been adjusted. Before performing the minimum idle speed adjustment, visually inspect the vacuum hoses for leaks, splits or cuts, the throttle body and intake manifold for vacuum leaks. Vacuum leaks can cause the engine(s) to run at a high rpm.

ELECTRONIC FUEL INJECTION

  1. Using a scratch awl, pierce and pry the idle speed screw plug from the throttle body; it can be discarded and not replaced.
  2.  
  3. Connect a tachometer to the engine. Set the parking brake, place the transaxle in the PARK , position the steering wheel in the STRAIGHT AHEAD position and turn OFF the air conditioning and all accessories.
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  5. Operate the engine until normal operating temperatures are reached.
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  7. Check and/or adjust the timing.
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  9. On the Climate Control Driver Information Console (CCDIC), press the "COOLER" button and wait for at least 20 seconds; this will cause the ISC motor plunger to retract. Once the motor has retracted, inspect the throttle lever to make sure it is resting on the minimum idle speed screw.
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  11. If the minimum idle speed it too high, use a T-20 Torx® Driver to adjust the minimum idle speed screw. The minimum idle speed should be 450-550 rpm (0-500 miles) or 450-600 rpm (above 500 miles).
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  13. After adjustment, disconnect the test equipment and turn the ignition switch OFF for 10 seconds.
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  15. Turn the engine ON , check the ISC operation and inspect the ECM and/or BCM readout for stored codes or telltale lights. Perform the diagnostics.
  16.  
  17. Disconnect the negative battery cable for 10 seconds; this will reset the TPS learned value in the ECM.
  18.  

DIGITAL FUEL INJECTION (DFI)



  1. Connect a tachometer to the engine. Set the parking brake, place the transaxle in the PARK , position the steering wheel in the STRAIGHT AHEAD position. Turn OFF the air conditioning and all accessories. Ground the green test connector located near the alternator.
  2.  
  3. Start and run the engine until normal operating temperatures are reached.
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  5. Check and/or adjust the timing.
  6.  
  7. Remove the air cleaner and plug the THERMAC vacuum tap.
  8.  
  9. To retract plunger of the ISC motor, perform the following procedures.
    1. Disengage the ISC connector, then engage a jumper harness to the ISC.
    2.  
    3. Connect the jumper wire leading to the ISC terminal C to 12V at the battery or junction block.
    4.  
    5. Apply finger pressure to the ISC plunger (close the throttle switch). Touch the jumper wire connected to the ISC terminal D to ground until the ISC plunger retracts fully and stops; DO NOT allow the ground wire to be connected for longer than necessary or damage to the ISC motor can result.
    6.  
    7. Once the motor has retracted, inspect the throttle lever to make sure it is resting on the minimum idle speed screw.
    8.  

  10.  

Never connect a voltage source to the ISC motor terminals A and B as damage to the internal throttle switch contacts will result.

  1. If the minimum idle speed it too high, adjust the minimum idle speed screw. The minimum idle speed should be 375-500 rpm (0-500 miles) or 475-550 rpm (above 500 miles).
  2.  
  3. After adjustment, disconnect the test equipment and turn the ignition switch OFF for 10 seconds.
  4.  
  5. Turn the engine ON , check the ISC operation and inspect the ECM and/or BCM readout for stored codes or telltale lights. Perform the diagnostics.
  6.  
  7. Disconnect the negative battery cable for 10 seconds; this will reset the TPS learned value in the ECM.
  8.  

DIESEL FUEL INJECTION



Idle Speed Adjustment

See Figure 1

A special tachometer with an RPM counter suitable for the 350 V8 diesel is necessary for this adjustment; a standard tach suitable for gasoline engines will not work.



Click image to see an enlarged view

Fig. Fig. 1: Diesel injection pump slow idle screw

  1. Place the transmission in Park, block the rear wheels and firmly set the parking brake.
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  3. If necessary, adjust the throttle linkage as described in Fuel System .
  4.  
  5. Start the engine and allow it to warm up for 10-15 minutes.
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  7. Shut off the engine and remove the air cleaner.
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  9. Clean off any grime from the timing probe holder on the front cover; also clean off the crankshaft balancer rim.
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  11. Install the magnetic probe end of the tachometer fully into the timing probe holder. Complete the remaining tachometer connections according to the tach manufacturer's instructions.
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  13. Disconnect the two-lead connector from the generator.
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  15. Make sure all electrical accessories are OFF.
  16.  

At no time should either the steering wheel or the brake pedal be touched.

  1. Start the engine and place the transmission in Drive (after first making sure the parking brake is firmly applied).
  2.  
  3. Check the slow idle speed reading against the one printed on the underhood emissions sticker. Reset if necessary.
  4.  
  5. Unplug the connector from the fast idle cold advance (engine temperature) switch, and install a jumper wire between the connector terminals.
  6.  


WARNING
DO NOT allow the jumper to ground.

  1. Check the fast idle speed and, if necessary, reset according to the specification printed on the underhood emissions sticker.
  2.  
  3. Remove the jumper wire and reconnect it to the temperature switch.
  4.  
  5. Recheck the slow idle speed and reset if necessary.
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  7. Shut off the engine.
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  9. Reconnect the leads at the generator and A/C compressor.
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  11. Disconnect and remove the tachometer.
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  13. If the car is equipped with cruise control, adjust the servo throttle rod to minimum slack, then put the clip in the first free hole closest to the bellcrank or throttle lever.
  14.  
  15. Install the air cleaner.
  16.  

 
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