The Surface temperature on Pluto itself varies between -240 to -218C because pluto itself is 10x further away from the sun than Neptune.
Due to orbital eccentricity the distance between pluto and the sun changes overtime and pluto itself takes over 240 years to make 1 revolution because pluto itself has an average speed of 10623 mph (17096 km/h) and because pluto itself is 5.9 billion kilometers away the sun itself and due to that amount distance (Either/Neither if it is now in the Orbit of Neptune) is the one that makes pluto cold.