Help to maintenance or test Sunfire 2002 sensor's

[orangel]

Hi

I have a sunfire 2002 2.2L and I observed an important diminution in the gasoline yield and power, the use and routes are the same, I changed all filters (gas, air) and the condition is same, the car have 55000Km.

1.- it wanted to know if he is recommendable resete or to reinitiate the computer to its original values.

2.- exists some form to give maintenance to the sensors for this model? , some form to verify its correct operation without the scanner? , some Link where can find diagram of the location the different sensors and their use for this model?.

3.- Some form to correct the gas mix.

4.- Tips to correct the problem.