Hey everyone. I got an SES light on my 2005 infiniti g35 coupe, 110k miles. I recently had my clutch replaced, and the technician was saying he was having trouble getting the SES light to turn off, due to a problem with the camhsaft sensor. However, he had said it was fixed and my car was all good to go. I picked it up and it ran fine. I had about a month of driving, and then the SES light came back on. I pulled the codes with a simple OBD reader, and i got the following:

1)P0174 - System Too Lean (Bank 2)
2)P0011 - Intake Valve Timing Control Performance Bank 1
3)P0021 - Intake Valve Timing Control Performance Bank 2

I hate to take my car to mechanics and even worse, the dealership, but I am lost on what to do now. I have read many things online saying that these codes could mean 100 different things need replacing. I am pretty much asking, what steps should i take from here? I enjoy doing my own car work, so anything that is not too extensive I would like to handle myself. Anyone have experience with these codes and how did you fix them?