visit Toyota 3S and get a detailed scanning & print out. to check correct average top up tank from a fuel dispenser reset trip meter and use car till such time the fuel alert lamp is on go back to same station same dispenser nozzle & top up again note the trip meter do some maths. do the ritual for 3 tank fills and that will give you per liter km average. Onboard computer get a ping from ecu every 180 seconds to calculate fuel consumption, reliable only over highways steady speed commuting
spark plugs other than the OEM specs are useless and waste of money. change of ONLY plugs does not improve the PERFORMANCE that is basless non-sense $hit myth created to make money.