I checked the engine codes, And surprisingly I have 3. 31, 34, 37
-Throttle Position Sensor or Circuit
-EGR Solenoid or Circuit
-O2 Sensor No. 2

Can somebody give me some advice on the codes and what can be done??

Also I was going to tighten my belt, which bolt do you tight. I see two near the radiator on the right side of the pulley system. One on top and one on bottom, I was guessing the bottom one but I wanted someones input. Thanx in advance guys.