04 elentra 2.0L Manual: Annoying Issues

I have a few issues with my 04 hyundai elantra 2L. my car stick on its revs randomly and starts revving on its own. i cleaned out my throttle body but it still does it. also the plate does not move while this is happening and neither is the throttle cable (meaning no tension). It's very scary and extremely annoying. sometimes when i give it a quick shot it'll stop it from revving but it sometimes doesn't Help? My third gear always Grinds when i shift into it no matter what i do. I always depress my clutch properly and try different ways as well as shifting at different RPMs to see if i can get it to go into smoothly but it always grinds. Their is no problems with the clutch either. I need help because i'd rather not send it to the mechanics unless i have no other choice! help!