The stepper motor is a multiphase driven motor from the ECU - you can not just unplug it and inject 12V for testing [8)]
But you can visually ensure the throttle flap/axle is not binding - thus giving the impression the stepper motor won't retract.
I'm a bit suspicious that your problem MAY be caused by a common serviceable mechanical problem - won't cost you much time to try solve it.
Testing the stepper motor on a 1.8i 16v
Moderator: RichardW
Definately understand why you keep asking [;)]
hmmmm ... [8)]
The stepper motor controls the engine idle revs ...
The engine temp sensor signals the ECU if the engine needs higher idle revs (& richer mix) ...
This sensor is a NTC resistor with high resistance at cold.
It's got a 2pole blue or green connector piece - should be located near the thermostat housing - or somewhere in the cooling waterways.
Note that the standard panel warning lamp sensors are single pole sensors only.
With warm engine - if you unplug the temp sensor - you then signal the ECU a "false" cold engine as the disrupted sensor equals a very lo temp. This should in turn make the ECU signal the stepper motor to open the throttle flap.
Of course the engine may get into trouble - suddenly having too rich warm idle mixture - but that's not the point here.
If you then unplug/reseat the temp sensor connector - you should then be able to "work out" the stepper motor.
Then it's up to you to decide if the stepper motor has a hard job moving - thus requiring service or replacement.
On the other hand - it would be interesting if this testing reveals other strange behaviour not expected.
hmmmm ... [8)]
The stepper motor controls the engine idle revs ...
The engine temp sensor signals the ECU if the engine needs higher idle revs (& richer mix) ...
This sensor is a NTC resistor with high resistance at cold.
It's got a 2pole blue or green connector piece - should be located near the thermostat housing - or somewhere in the cooling waterways.
Note that the standard panel warning lamp sensors are single pole sensors only.
With warm engine - if you unplug the temp sensor - you then signal the ECU a "false" cold engine as the disrupted sensor equals a very lo temp. This should in turn make the ECU signal the stepper motor to open the throttle flap.
Of course the engine may get into trouble - suddenly having too rich warm idle mixture - but that's not the point here.
If you then unplug/reseat the temp sensor connector - you should then be able to "work out" the stepper motor.
Then it's up to you to decide if the stepper motor has a hard job moving - thus requiring service or replacement.
On the other hand - it would be interesting if this testing reveals other strange behaviour not expected.