argonweld

hi all,
eng temp sensor on own diagnostics 21.i have been operating on octane boost with unleaded as super not readily available.i can only start with two dips of accelerator with key off.scooby then starts,it will run faster than normal 4 a moment,i can then drive and after half mile cel comes on feels like driving on 3 pots,400 yards later cel goes off and engine perfect no more cels
is this fuel or a problem because of eng temp sensor,if latter how do i replace and exact location please.i have 1994 scooby imp turbo wrx import,is eng temp sensor showing me permantely hot!!!