A lot would depend on the outside temperature, and driving conditions .
Given a situation where , you were at idle or coasting for an extended time , in cold temperatures, and then accelerated, there could be enough cold air get into the intake manifold to trigger an intake heater cycle.
If you were holding a constant speed in temperatures above 50f, then good chance you have a defective " intake manifold temperature sensor ".
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.