1994 mitsubishi lancer coughs and surges

i have a 1994 mitsubishi lancer 1.8l efi. when driving, especially from a standing start, the car coughs and surges. while parked if i put my foot to the floor quickly the car struggles to get revs but if i slowly rev it its fine. a bloke i no sed it could be a spark problem so i replaced the plugs, leads, distributor cap and fuel filter. the coil and rotor button were also replaced 18 months ago.