Fault Code 25


Description:  AIS (Automatic Idle Speed) motor circuit shorted or target idle speed not reached
Power loss light:  Off
Limp-in mode:  None

Possible Causes

Vaccum leak - Check all vaccum lines for cracks or breaks.

Bad connection or wiring - Check the wiring and connections between the logic module and the motor.  Clean and regrease any corroded connectors with dielectric grease and repair any shorts.

Shorted or frozen AIS motor - The AIS motor is located near the TPS.  For 1987 or earlier Turbo I engines, remove the bolt and slide the motor out (you may have to wiggle and twist it).  Remove the clamp and carefully pull out the motor.  Be sure and observe how it goes together, especially the orienation of the rotatiing valve inside.  Hook the motor to a 12V supply to see if it runs.  If it doesn't, replace the AIS.  Clean all the gears and shafts throughly and reassemble the gear and valve assembly.  Spray all the gears and parts with TriFlo or a similar silicone spray lubricant (don't use WD40 because it evaporates) and insert the motor.  If the engine seems to race wildly after assembly (give it some time to get control), you probably installed the internal, rotating valve backwards.

Diagnostic Method

Trigger Parameters

- Near 0V or near 12V not detected when the motor driver is turned on or off, respectively


- Target idle speed not reached after a number of attempts

Results If Component Fails

Fault code 33 is stored.


The logic module cannot detect an open circuit in the wiring, so a fault code may not be stored on vehicles (unknown which) with logic modules that don't keep track of how many times it has tried to adjust the idle.
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This page is maintained by Russell W. Knize and was last updated 08/28/98. Comments? Questions? Send email.

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