2005 Altima 3.5 with DTC P0300 & P0011

[2001I30MAX]

On 2005 Altima 3.5, with 110k miles, I have 2 codes (p0300 & p0011) and I am trying to narrow down possible causes. I searched this forum and also looked at the FSM on possible causes of p0011. Although the engine oil was changed about 3 months ago, I changed it again yesterday. Within, say 1 hour of driving, the SEL light came back on with the same codes as before. My next attempt is to check the sensors (Cam and Crankshaft position) but I read these sensors are located in hard-to-reach area and I am trying to minimize my work.

I want to know if anyone had any experience with this combo of codes and how they went about narrowing down the causes.

Further, if I have to replace IVT Control valve/system for DTC p0011, I would like to know if this is DIY or dealer job, and the cost of the repair.

Thanks in advance for your input.