Speed Adjusting Screw

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The following procedure is from the factory service manual. For our purposes, replace the use of the factory scantool MB991958 with a datalogger with actuator control, such as EvoScan, or one which allows arbitrary commands to be sent (see the MUT Commands page for the command ID to send for SAS control).

Adjustment Procedure

NOTE: The standard idle speed has been adjusted with the speed adjusting screw (SAS), by the manufacturer, and there should be no need for readjustment.

NOTE: If the adjustment has been changed by mistake, the idle speed may become too high or the idle speed may drop too low when loads A/C, defogger, etc. are placed on the engine. If this occurs, adjust by the following procedure.

NOTE: The adjustment, if made, should be made after first confirming that the spark plugs, the injectors, the idle air control motor, compression, etc., are all normal.

  1. The vehicle should be prepared as follows before the inspection and adjustment.
    • Engine coolant temperature: 80 − 95°C (176 − 203°F)
    • Lights, electric cooling fan and accessories: OFF
    • Transaxle: Neutral
  2. Connect scan tool MB991958 to the data link connector (16-pin). CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
  3. Start the engine and run at idle.
  4. Select the item number 30 of the scan tool Actuator test. NOTE: Use the scan tool to hold the IAC motor at the basic step to adjust the basic idle speed.
  5. Check the idle speed. Standard value: 850 ± 50 r/min

NOTE: The engine speed may be 20 to 100 r/min lower than indicated above for a new vehicle [driven approximately 500 km (300 mile) or less], but no adjustment is necessary.

NOTE: If the engine stalls or the engine speed is low even though the vehicle has been driven approximately 500 km (300 mile) or more, it is probable that deposits are adhered to the throttle valve, so clean it. (Refer to P.13A-813.)