temp sensor help
 

i have a 2001 s-10 blazer 4wd with a 4.3 and im having a trouble code. its po117- engine cooloant temp circuit low imput. i replaced the sensor with a new one and erased the code and same problem still. The temp gauge and rpm gauge both jump up and down. temp gauge goes up to full temp then to normal. sometimes it dont move at all. anyone have any ideas what could be causing this?