Hesitation, rough idle, loss of acceleration, and similar symptoms can be caused by many issues, only some of which can be addressed with a fuel additive. To ensure you’re maximizing the effectiveness of such an additive, we recommend using Berryman B-12 Chemtool Total Fuel System Clean-Up (part #2616), which contains our strongest detergent package and powerful high-energy solvent technology or “H.E.S.T.”-based solvents. For greatest efficacy, use 2616 at 1 oz/gal of gasoline. You might also check the appearance of the throttle body. If there is substantial carbon buildup on the butterfly, that could be contributing to the problem by impeding proper airflow. Berryman B-12 Chemtool Carburetor, Choke & Throttle Body Cleaners (part #s 0117 and 0117C) contain H.E.S.T. solvents to dissolve such buildup. If the combination of the fuel additive and the carb spray do not improve the performance of your Highlander, then your condition is likely mechanical (fuel pump, fuel filter, failing injector, etc.). Best of luck!