someone please advise...i had my merc serviced last month..just a general full service from an independent garage... after a few days the car was idling and very sluggish with no power...i returned it to the same garage and his diagontic tool indicated the mass air flow and oxygen sensor were faulty..had those changed...resulting in aproxx 85% improvement..but the last 3 full tanks, i an getting only 220 miles to previously, aprox. 330 miles..i am taking back to the garage, but can anyone advise any tips to what is causing this...thanks
