Ha ha. This happened to me 1.25 zetec Fiesta and it turned out to be a dirty MAF sensor. This is located in the metal bit closest to your air filter. A cotton swab with some meths on should do the job. Mine reduced in size about 10times after cleaning. Just be careful you don't use too much pressure as it's quite 'dainty'.

My car ran like a dream afterwards.


Hope this helps you!


Pete.