New CTS required?

[dvhttn]

Recently the glowplug light has been taking longer to go out (outside temperature has no effect - been doing it whatever the temp. is even the recent mild weather) and the idle speed seems high for a couple of seconds before settling down. I'm thinking the CTS needs renewing? It was last done nearly 6 years ago and a genuine green one fitted. Sound plausible? If so I'd replace the thermostat at the same time and I might even combine it with a turbo out/inspect and clean to kill several birds with one stone.