Nissan Repair Questions? Ask a Mechanic for Answers ASAP
The code P0300 is a "Random/multiple misfire" and the P0011 is a code for a cam position sensor failure.
The Altima is well known for prematurely failing cam and crank position sensors. Both should be replaced at the same time; when one fails, the other one is not far behind since they both live in an identical environment with heat and vibration present.
The sensors are identical, they even have the same part number.
When the cam sensor starts acting up, it sends wrong cam timing information to the computer, which then may fire the spark at the wrong time or not at all. This can trigger the P0300 misfire code.
While you may indeed need a tune up (new sparkplugs, pull one out and see if it looks old or worn), I would start with the cam sensor, then crank sensor, and clear the codes, see how it behaves on a test drive.
The cam position sensor is easier to replace than the crank sensor, you may want to start with that alone. There's two cam sensors on the V6, your code indicates the Bank 1 sensor is causing trouble, that's the cylinder head closest to the firewall.
The crank position sensor is on the engine block also on the firewall side, tucked up next to the starter, and somewhat hard to reach, especially without a lift.
Once you replace the cam position sensor, the "misfire" will probably go away on it's own. let me know if you need further assistance!