Renegade acceleration problems

Hi this is my first time trying to post something here. I have a 2008 renegade 800 that I got a few weeks ago and I’m having some problems with it. First it seams like it accelerates by it self. When I have it on reverse or high or low it whants to go by it self. I adjusted the throttle cable by the handle bar and it helped some but when I put it in nuetrol it reves up again. What could it be? I fist though it was the shifter pulling the cable so I moved it and it did the same thing. Is there something I’m overlooking? Second problem is that when it sits for a few minutes it starts to over heat. I’ve heard that taking the thermostat out will help but I didn’t want to take things out without double checking first. I would really appreciate y’all thoughts. Thanks guys.