Assuming as MY99-00 (or new age)
Resetting the ecu restores the default settings, one of those is the Advance Multiplier (AM) which is reset to 8, if the ecu had pulled ign and the AM had fallen to below 3 then the boost would have been cut to actuator pressure and the ecu will have been using the high det fuel maps which are richer for safety. Default is AM 8 which runs the car on normal bost control and normal fuel maps. It can then be remapped to maintain the settings but you won't have the best from it if it was mapped on incorrect fuel.

The same principles apply to the earlier ecu's.

bob

Thanks for that info Bob. :)
I forgot some info for you, my car is a new age, MY03 WRX.
Although it feels fine (i want more!), it does only RR at 268 bhp and 266 ib/ft, which for the mods is slightly lower than most i see on here. Like you mentioned Bob, that could purely be down to the fuel and or the map itself.
The first RR i had did actually show a "safe" remap in that the fuelling is rich at high revs, and the RR guy said they normally map just a little leaner.
I am like most on here now, i want more! LOL.
Trouble is, i want MY06 T25 more! Hahaha.

maf
 

thanks bob.i took the air intake apart today and everything looks perfectly clean to me the air filter looks like new and so does the maf,the gauze looks a little dirty so i will clean it tommorrow apart from that its all ok.is there anything else you suggest i should look at which could be the cause of the missfire.it only happens when the engine is warm/hot.could it be that i am hitting fuel cut from overboost being caused by a dirty/faulty boost control solenoid or am i barking up the wrong tree? (i just came to that conclusion by reading through post on here).cheers mate.