2003 Other Ford Models misfire

I have an 03 fiesta zetec 1.4 she started stuttering and misfiring and theres was a serious loss in power. The orange engine light has come on and when I try revving her the light starts to flash. My first thought was that the spark plugs needed chaging so I have done that along with a full service, including changing the air, oil, pollen and fuel filter and replaced the oil, but she is still missing and stuttering. Do u ave any idea of wot the problem could be?
thank you for taking the time to read this and I look forward to hearing from you.

mike rees