I have 2 codes showing and I've been trying to figure out what to replace or what to do to fix these problems. The one is saying the mass air flow sensor which I recently replaced and checked it the other day and still like new. The other is saying an o2 sensor but lists different things that could cause that code to fire.

 

A vacuum leak can cause those 2 codes. Carefully check all your hoses. Put a vacuum gauge in place of the small vacuum hose coming off the intake to the vacuum reservoir canister. It should read in the mid teens and be steady.