i think you'll find you need to re set the ecu, then run the car for about 30 miles to set the system up to the new filter. when you fitted it, did you take the fuse out of the ecu?

1998 mondeo st24 juice green,ramair filter, urban chrome matrix alloys 17", twin headlights, black rear lexus lights, smoked side repeaters, twin single exit duel exhaust, sony ice,gas bonnet struts, shiny engine bits, st24 door sill protectors,