Misfire problem

[barrel24]

Hi I have a 55 plate petrol 1.6 vvt dynamique sport tourer with a problem every now and again the engine light and service light comes on I have had it read and it comes up #4 cylinder misfire but the car isn't running rough and fuel consumption hasn't gone down however if I run a bottle of redex through it the light goes off after about 100 miles and stays off for about 1-2 tanks of fuel (without redex) then comes back on I have changed the coils and this sorted it for a little while but now it's back and I'm starting to think injectors any ideas many thanks chris