Hotend does not reach set temperature
Your description sounds indeed as if the PID is not correct. You can try autotune with M303 only if your heating cartridge is not absolutely overpowered. However, in such a case you typically also have an overshoot, which you don't mention in your description. 

In that case you need to lower your duty cycle (by the BANG_MAX parameter in the firmware) a bit. Otherwise autotune fails, because your heating cartridge overshoots even at small gains.

Out of the box I would suggest you to increase your D-term and decrease your I term if it cycles like that. For most printers, I used, a ratio like that is sufficient: 4/1.5/25.