How To Install Fox Body IAC Adjuster & Set Mustang Idle

Posted 12/14/2016 by Tyler Rodriquez

Follow along as we walk you through installing a Idle Air Control Adjuster in your 1986-1993 5.0L Fox Body Mustang!

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The Idle Air Control Adjuster spacer service kit is used to correct sludge contamination concerns of the throttle bore and plate only. Verify that the idle speed concern is not being caused by the fuel system, IABP solenoid, throttle linkage, ignition system, PVC system, EGR system, cooling system, or vacuum leaks before proceeding with the installation of this idle air adjuster.

Installation Instructions

  1. Turn engine off, put transmission in park, engage parking brake, and block wheels. Disconnect all cables from the throttle control arm and disconnect the IABP solenoid connector.

  2. Do not clean the throttle bore/plate area.Removing the sludge accumulation in the throttle bore will reduce the effectiveness of the idle air adjust spacer.

  3. Adjust the throttle plate position in the throttle bore to minimize closed plate air flow by turning the throttle plate stop screw on the throttle body counterclockwise until it is no longer in contact with the throttle control arm stop. gently cycle the throttle plate open and closed a few times to ensure the throttle plate is at the full closed position. Place a 0.002" feeler gauge between the stop screw and throttle control arm and adjust the screw clockwise until it just contacts the feeler gauge. Remove the feel gauge and turn the screw clockwise an additional 1/2 turn.

  4. Snap the throttle from open to closed several times to make sure the throttle plate does not stick, bind or grab in the bore.(if necessary, continue clockwise adjustment of the throttle stop screw for the minimum amount required to eliminate the stick/bind/grab condition.) Run KOEO self-test to verify that no TPS fault codes exist once throttle plate adjustment is completed.

  5. Remove the IABP solenoid and discard told gasket. Note the position of the solenoid connector before removing so that it can be replaced with the same orientation. (IABP solenoid mounting location varies depending on model year and engine application. Reference appropriate engine shop manual for location)

  6. The Idle Air Adjuster Spacer comes preset at maximum air flow for engine applications of 5.0L displacement and smaller. Any engine with a displacement larger than 5.0L (such as a stroker or 5.8L based engine) require additional air flow. It is necessary to remove the cup plug (see diagram) prior to installation on the engine. To remove the cup plug, use a center punch and tap lightly from the bottom side of the cup plug to pop it out. Discard the cup plug.

  7. Install Idle Air Adjuster between IABP solenoid and engine mounting location.

  8. Important: Install the Spacer so that the spacer port with the trim screw keyways aligns with the clean air port of the mount.
    NOTE:Replace the two short existing IABP solenoid bolts with the longer bolts provided in the kit. On applications that use a stud r, reuse the stud and use only one new bolt.
    NOTE:On engine applications that see IABP solenoids with the three mounting bolts, use one of the short existing bolts to plug the third tapped hole and mount the solenoid/spacer assembly using the two longer bolts provided with this kit.

  9. Torque bolts to 6-8.5lbs-ft.

  10. Reconnect the cables to the throttle control arm.

  11. Refer to the appropriate engine/emissions diagnosis shop manual for the proper EFI engine idle speed adjust procedure. Follow the procedure specified for the vehicle/engine combination being serviced except: do not turn the throttle plate stop screw. Adjust the idle speed by turning one or both spacer trim screws using a 2.5mm allen wrench (turn clockwise to decrease RPM and counterclockwise to increase RPM). Set the Engine speed to the high end of the specified range to prevent any future sludge build up from causing additional problems.

  12. NOTE: On applications that do not specify a RPM setting in the shop manual, adjust spacer trim screw to obtain 550 RPM in drive with the A/C off and ABP solenoid connector disconnected.
  13. Reconnect the connector to the IABP solenoid and verify the engine is idling properly.
  14. With the engine running, cycle the throttle several times to verify that the plate does not stick, bind or grab.

From Ford Performance: 1986-1995 Mustang Idle Setting Procedure

Please Note: These steps MUST be performed in sequence!!

  1. Get engine to operating temperature.
  2. Disconnect IAC (Idle Air Control) Solenoid. If engine stalls, turn throttle-stop screw in one full turn and restart. Repeat as necessary until engine will idle with IAC unplugged.
  3. Set idle using throttle stop. Idle speed will vary depending upon modifications made to the engine. Set to where you are comfortable with idle speed.
  4. Set TPS (Throttle Position Sensor) anywhere from .96 to .98 volts. This is done by loosening the mounting screws, and lightly rotating TPS. If you cannot obtain the desired range, you may need to make the mounting holes slightly larger. This can be done by drilling them.
  5. TPS wire colors to be probed are generally BLACK and GREEN wire or the GRAY/RED and GRAY/WHITE, depending on your vehicle.
  6. Stop engine. Disconnect negative terminal battery cable for 15-20 minutes. You may wish to tap the brakes or turn the headlights on and off a few times as this will help to ensure that you have purged any remaining electrical current from the vehicle.
  7. Reconnect IAC Solenoid
  8. Reconnect battery cable to the negative terminal
  9. Restart engine.
  10. If problem persists, inspect for mass air meter problems and possible vacuum leaks.

  • 1986-1993 Mustang EFI V8 Idle Air Control (IAC) Adjuster - by 5.0 Resto

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