I have a 2002 GS300 with 131,000 miles on it. I am an original owner and have kept the car in fairly good shape. I want to do a standard tune-up to improve the performance, but need to know what the common check points should be on a vehicle of this age. The car performs fairly well out on the road, but there are a few things i need of attention/maintenance. I experience a slight hesitation at times on acceleration. It also has a slightly rough idle on start-up. Once the car is on the road and warmed up, it turns into a small miss at a stoplight. Recently I changed the mass air sensor and intake air filter as a starting point, but really found not too much improvement. Appreciate any comments/suggestions on where to focus attention on tuning it up. Thank you in advance.

If the spark plugs have never been changed then I would do those along with wires. Your valve cover gasket could also be leaking which would cause the issue you're describing. Oil can start leaking into the center valley between the valve cover gaskets which then makes its way past the spark plugs affecting their ability to ignire the fuel and air.

You could also check the throttle body valve and clean that if it has carbon buildup.

If the timing belt has never been changed then that should be done asap along with the water pump.