Pontiac Fiero 1984-1988 Repair Guide

2.5L Engine

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1984-86 MODELS





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Fig. Fig. 1 Removal of the idle speed adjustment screw plug-1984-85 2.5L Throttle Body Injection (TBI) engines



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Fig. Fig. 2 Use tool J-33047/BT 8207-A to plug the passage-1984-TBI engines



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Fig. Fig. 3 The Idle Air Control (IAC) identification

These adjustments are controlled by the Electronic Control Module (ECM). No adjustments are necessary unless the throttle body assembly has been replaced. Below is the procedure for adjusting the idle speed.

The throttle stop screw is used for regulating minimum idle speed and the adjustment is factory set. The screw is covered with a plug to discourage unauthorized adjustments. However, i it is necessary to gain access to the idle stop screw, the following procedures eliminate the need to remove the throttle body from the manifold.


CAUTION
To prevent the engine from running at high rpm, make sure the ignition is OFF and the vehicle is in NEUTRAL before connecting the Idle Air Control (IAC) valve. Failure to do so may result in the vehicle moving.

  1. Disconnect the negative (-) battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Use a prick punch to establish a location over center line of the idle stop screw so a hole can be drilled. Refer to the idle stop screw removal illustration in this section.
  6.  
  7. Drill a 4mm diameter hole through the throttle body casting to the hardened plug and stop.
  8.  
  9. Use a 2mm diameter punch to drive through the bottom of the drilled hole and knock out the plug.
  10.  

To adjust:
  1. Remove the throttle valve cable from the throttle control bracket to allow access to the minimum air adjustment screw (auto trans only).
  2.  
  3. Set the parking brake and block drive wheels. Connect a tachometer to the engine at the distributor (TACH) terminal.
  4.  
  5. Disconnect the Idle Air Control (IAC) valve electrical connector. Refer to the exploded view of the throttle body assembly for IAC valve location.
  6.  
  7. Start the engine, put transaxle selector in PARK (NEUTRAL on manual trans) and allow the rpm to stabilize.
  8.  
  9. Install a J-33047 plug in the idle air passage of the throttle body. Seat the tool in the air passage until it is bottomed and no air leaks exist.
  10.  
  11. Using a No. 20 Torx® bit, turn the idle speed stop screw until the engine rpm is 500 - 25 for the 2.5L with automatic transaxle and 775 - 25 rpm for the 2.5L with manual transaxle.
  12.  
  13. Stop the engine and remove the tool from the throttle body.
  14.  

To install:

  1. Install the throttle valve cable into the throttle control bracket (auto trans only). Reconnect the IAC valve electrical connector.
  2.  
  3. Seal the drilled hole in the throttle body casting with silicone sealant or equivalent and install the air cleaner.
  4.  

1987-88 MODELS





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Fig. Fig. 4 Use an awl to pierce and remove the idle speed adjustment stop screw-1987-88 2.5L TBI engines



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Fig. Fig. 5 The Idle Air Control (IAC) valve is located on the lower side of the throttle body assembly-1987-88 2.5L TBI engines



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Fig. Fig. 6 The Assembly Line Diagnostic Link (ALDL) is located in the passenger compartment console

These adjustments are controlled by the Electronic Control Module (ECM). No adjustments are necessary unless the throttle body assembly has been replaced. Below is the procedure for adjusting the idle speed.

The throttle stop screw is used for regulating minimum idle speed and the adjustment is factory set. The screw is covered with a plug to discourage unauthorized adjustments. However, if it is necessary to gain access to the idle stop screw, the following procedures eliminate the need to remove the throttle body from the manifold.


CAUTION
To prevent the engine from running at high rpm, make sure the ignition is OFF and the vehicle is in NEUTRAL before connecting the IAC (Idle Air Control) valve. Failure to do so may result in the vehicle moving.

  1. Start the engine and run until it reaches normal operating temperature. Then turn the ignition OFF.
  2.  
  3. Remove the air cleaner and gasket.
  4.  
  5. Pierce the idle stop screw plug with an awle and apply leverage to remove it.
  6.  
  7. Connect a suitable tachometer to the TACH terminal at the distributor.
  8.  
  9. With the idle air control (IAC) valve connected, ground the diagnostic terminal of the Assembly Line Diagnostic Link (ALDL) connector. Refer to "ALDL Connector Location" illustration in this section.
  10.  
  11. Turn the ignition ON, but do not start the engine. Wait at least 45 seconds.
  12.  
  13. With the ignition ON, engine not running, test terminal grounded, disconnect the IAC valve electrical connector.
  14.  
  15. Block the drive wheels and apply the emergency brake.
  16.  
  17. Remove the ground from the diagnostic terminal Assembly Line Diagnostic Link (ALDL) and START the engine.
  18.  
  19. Place the transaxle selector in the NEUTRAL position and allow the idle to stabilize.
  20.  
  21. Adjust the idle stop screw to obtain 600 - 25 rpm. Turn the ignition OFF and reconnect the IAC valve electrical connector.
  22.  
  23. Apply silicone sealant or equivalent to cover the idle stop screw and install the air cleaner assembly.
  24.  

 
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