hey there Mildwin, remember me??? LOL
since I last replied I have had a look at a newer model of fiesta than I had worked on before, and it had a poor idling speed! This is an L-reg 1.3l CFi engine.
I discovered there was an electrical device which controlled the idle speed (remember my query about Haynes showing an electrical connection in the circuit diagram but talking about a vacuum mechanism controlling the idle speed when drive is engaged). Haynes calls it a throttle plate control motor.
So now I know that there is an electrical device that sets the idle speed in conjunction with a mechanical pivotting arm, and so adjusting the throttle cable doesnt do as the previous posts say.
Haynes also says that setting the idle speed can only be done by a Ford dealer but its not true, I did reset the one I worked on and it worked fine.
The plunger in the throttle plate control motor which actually controls the throttle position in the carb should be able to move in and out, it is most noticeable when you release the accelerator pedal after revving the engine. When the pedal is pressed, the plunger is not in contact with the lever, this IS when the cable is in play. However, when you release the pedal, a spring pulls the throttle closed but the plunger then comes into play: the way it works is the engine speed drops BELOW idle speed for a few moments, and then the plunger gracefully slides out to set the idle speed where it should be. The plunger pushes on a circular pad that is on a threaded rod, which is screwed into the pivotting arm. There is a small hexagon (about 4 mm across flats) on the back of the threaded rod with the circular pad that the plunger touches, and this is what can be reset.
(Continued in next post)