u/North_Analyst_9987

HELP!! Any idea what the problem is? 2017 Highlander LE 23,000 miles. Recently was getting 19-20 mpg all short trips in warm weather. Had problems starting and mechanic found and fixed a vacuum leak. No more starting problems but gas mileage dropped to 12 miles per gallon. Put fuel system cleaner in gas tank, cleaned mass air flow sensor and throttle body. Replaced the engine and cabin air filters. Still 12 mpg! Mechanic now suggesting replacing the spark plugs and coils. But the vehicle runs strong with lots of power and no misfires.