As Holice first suggested:
Make sure your feed dogs are lowered/dropped or covered.
On my machine (a Pfaff 1471 - late 1980s machine), the instruction manual says for darning to lower the presser foot only 'half-way' for darning/FMQ. There is a 'stop' that I seldom use, but it is there - perhaps your machine also has the same feature?
Do you still have the operating instructions that came with your machine? There may be a section called "darning" that might give you suggestions on how to set up the machine.