hey all, i just bought a 2005 S40 2.4i - learning about the car as it is my second day with it. I wanted to know if I can set the computers language to English somehow. It is a quebec car and the main screen that tells you the door is open etc is in French. how can i make this English? couldn't find anything in the owners manual.

my next question - fuel economy - is there any harm in filling 87 octane and adding octane booster to it? or best to just go with 91 octane? i won't be doing long drives. and i have already noticed that the car has horrible city mileage. no way of finding out from the computer exactly how many L/100km im getting since i don't have the trip computer option..

i would also like to know if these 5cyl engines require special attention of any sort? i mean it turns on from a cold start like a champ. and gets to under 1000rpm within the first 30seconds. i dont think i have ever owned a car that does this (i have owned numerous mercedes, bmw, audi, nissan etc).
im wondering if adding stuff like Lucas oil / fuel injector treatment will help or cause issues? I recently got a System too lean error. P0171. this happened right after filling 87 octane - driving for 10km and when i got back into the car and fired it up - check engine light was on. got it cleared. and it hasn't returned since yesterday.

any tips or tricks you guys know about? thanks in advance for any replies
Happy Holidays + New years soon