bro first of all get the cars throttle body cleaned,get the air filter changed,oil and oil filter changed,auto transmission oil and filter changed,fuel filter changed and fuel pump checked (pressure test) besides that get new spark plugs! and get the injectors cleaned thru ultra sonic process.
and stop driving the car on hi octane since hi octane is meant for high compression engines and not 1300cc 1500cc engines coz hi octane burns slowly! just drive it on normal super petrol frm caltex!