my 93 wrx import runs a bit rough and sometimes does not boost properly, you some times have to back off and then go again to get it to boost, iv alresdy tried a lamba sensor and another set of coil packs as two of the old ones had cracked, also could you tell me what a maf sensor is could this be my problem

 

what type of petrol you using

should be at least 98 ron and if possible octane boost of some sort
optimax seems to be best