First;
I am replacing my "2nd O2 sensor". How do I know which this one is? The one closest to the engine or is it the one that is under the passenger seat?

Second;
On my air control, I can only use the highest air flow option (full blast blowing) or nothing at all. I cant figure out what I need to replace or what I need to do to resolve this issue.

Thanks for everyone's help. Here are some more of my car's specs.

-2000 Mercury Mystique
-V6

Need anymore info just let me know.