GM Caprice 1990-1993 Repair Guide

Fuel Injected Engines

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The fuel/air mixture is controlled by the ECM and is non-adjustable.

MINIMUM IDLE SPEED ADJUSTMENT



This adjustment should be performed only when throttle body parts have been replaced. Engine must be at normal operating temperature before making an adjustment.

Throttle Body Injection

See Figure 1



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Fig. Fig. 1: Throttle stop screw plug removal procedure - TBI Engine

  1. Using a suitable tool, pierce the idle stop screw plug and remove it. Plug any necessary vacuum ports and connect a tachometer to the engine.
  2.  
  3. With the IAC valve connected, ground the diagnostic terminal (ALDL connector).
  4.  
  5. Turn ignition switch to the ON position, but do not start the engine. Wait for at least 45 seconds, allowing the IAC valve pintle to fully extend and seat.
  6.  
  7. With the ignition switch still ON and test terminal grounded, disconnect Idle Air Control (IAC) electrical connector.
  8.  
  9. Remove the ground from diagnostic lead and start the engine.
  10.  
  11. Adjust the idle speed screw to obtain 400-450 rpm with the transmission in N .
  12.  
  13. Turn the ignition OFF and reconnect connector at IAC motor.
  14.  
  15. Adjust the Throttle Position Sensor (TPS) to specifications.
  16.  
  17. Recheck the setting, start the engine and check for proper idle operation.
  18.  

 
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