I Possibility of a heat soaked ACT sensor which will get moved this winter.
ACT sensors do not heat soak. They measure actual air temp, to a point. Anything beyond 255* or so the sensor stays pegged as it is out of range of the sensor to measure. As soon as ACT lowers to 254* it makes note of the change. I doubt that the air in your intake manifold goes beyond 255*, though it is possible under non intercooled boost conditions. If 255*+ was reached while under boost, as soon as you came off boost the air temp would drop back down.