Saturn Coupes/Sedans/Wagons 1991-1998 Repair Guide

Idle Speed and Mixture Adjustments



See Figures 1, 2, 3, 4 and 5

The idle stop screw controls the minimum idle speed of the engine, from which the PCM will raise idle speed as necessary for operating condition and load. The stop screw is preset at the factory and requires no periodic adjustments. Adjustments should be performed ONLY when the throttle body has been replaced and/or proper idle speed cannot be obtained. Be aware that improper adjustment of the minimum idle speed could result in false PCM trouble codes, idle instability and problems with shifting of the automatic transaxle.

The engine should be at normal operating temperature, the A/C and cooling fans should be OFF when making adjustments.

  1. Because residue accumulation can affect idle speed, clean the throttle body bore before making any adjustments. Use a clean rag and a carburetor cleaner that does not contain methyl ethyl ketone. Take extreme care not to scratch or damage the throttle body bore or valve. Then check the idle speed to be sure adjustment is necessary. Proper idle speeds are as follows:

    SOHC with manual or automatic transaxle in N-700-800 rpm
    SOHC with automatic transaxle in D-600-700 rpm
    SOHC with automatic transaxle in D and A/C ON-725-825 rpm
    DOHC with manual transaxle in N-800-900 rpm
    DOHC with automatic transaxle in D-700-800 rpm


  1. Block the wheels and apply the parking brake.
  3. Connect IAC tester SA9195E or equivalent to the IAC valve at the throttle body, a suitable scan tool to the diagnostic connector under the dash, or the equivalent of either to the appropriate location. Use the tool to bottom the IAC pintle in the throttle. If a scan tool was used, disconnect the IAC valve electrical connector after the pintle is bottomed to make sure it remains bottomed.
  5. Remove the idle stop screw plug or cover. For SOHC TBI engines only, remove the plug by piercing it with an awl and applying leverage. On DOHC and SOHC MFI engines, remove the idle stop screw cover.
  7. Insert the IAC air plug in the throttle body; use tool SA9196E for TBI or tool SA9106E for MFI or an equivalent plug.
  9. Connect the Saturn Portable Diagnostic Tool (PDT) or equivalent scan tool to the Assembly Line Diagnostic Link (ALDL) located under the dash, start the engine and check the minimum idle speed. Minimum idle speed should be 450-650 rpm for all engines.
  11. If not within specification, adjust the idle screw to obtain a minimum idle speed of 500-600 rpm.
  13. Turn the ignition OFF and reconnect the IAC electrical connector.
  15. Using the scan tool, check the TPS voltage. Do not replace the TPS unless its reading is not between 0.35-0.70 volts.
  17. Remove the IAC air plug and install the idle stop plug or cover.
  19. Start the engine and check for proper idle operation.
  21. Shut the engine OFF and remove the scan tool.

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Fig. Fig. 1: Connect the IAC valve tester to the valve terminal

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Fig. Fig. 2: Pierce the idle stop screw plug with an awl and remove-SOHC TBI engine

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Fig. Fig. 3: Idle stop screw cover location-DOHC engine

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Fig. Fig. 4: Insert the IAC air plug into the throttle body

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Fig. Fig. 5: Connecting the Saturn PDT or an equivalent scan tool to the ALDL


The air/fuel mixture is controlled by the Powertrain Control Module (PCM) during all modes of operation; therefore, no idle mixture adjustment is necessary or possible. For more information, refer to Fuel System of this guide.