Hi i have a 2001 bugeye wrx its got turbo back exhaust/3port solenoid/panel filter/ngk 8 plugs/alloy rad/forge d.v./uprated fuel pump/ & been mapped by v.good mapper,now for last 9months or so it drives like its standard then once in a while it will go absolutely great as it ment too,when i had a map tweak last time the mapper ask had i used a different fuel or done something else to it as he got another 3degree's of timing & car went fantastic then next day it drove crap again,it idles fine there's no cel at mo,i did get cel for front o2 sensor & replaced with denso sensor thought this was going to solve the problem but still no joy,there is one other cel i got the day before i first got it remapped which was 0420 but mapper said no probs as he was turning off the rear sensor,but it got to a point were its only getting 20mpg max on a run taking it real easy when i was getting real good mpg,i just dont no what to try next help please?