how can i fix my 1996 1.1 fiesta?

There are a number of reasons why this could occur but without a fault code reader it is hard to pinpoint exactly!

One possible reason would be the throttle position sensor giving an incorrect output to the ECU.. usually associated with poor starting also!
To test the TPS locate the 3 pin multiplug near the CFI unit and with a volt meter set to DC volts check the voltage at the brown/green wire with the ignition ON/engine OFF it should red approx 0.8 volts throttle shut and rise fluidly to approx 4.8 volts throttle wide open.
The DCICV (stepper motor) could also have a fault this unit has 2 functions as it not only maintains a set idle speed it also senses when the throttle is closed/open. to test this idle switch locate the 4 pin multiplug near the unit and disconnect it, with a volt meter check for contiuity on the wires in the multiplug(stepper motor side) which correspond with the brown and brown/yellow of the vehicle loom side, you should have open cicuit then closed cicuit with the throttle being operated from closed to open and visa versa.Have the ignition OFF.
Hope you fix

tony
February 2004