so i have a 99 ford ranger 6cyl 3.0 manual trans. lately every time i push in the clutch to shift the rpms stay high. it used to do it every now and then now its whenever the engine warms up or u drive for a while. i changed the idle valve and it still did it. i tried cleaning the throttle body and still no change. someone plz help!!! is it bad for my truck??? will it hurt the engine???