Thermo Control Element The TCE, also referred to as the wax pellet, is located on the base of the of the throttle chamber and controls cold start idle. As the pellet expands as the engine warms up it lowers the mechanical idle. Over time the o-ring that seals them tends to start leaking coolant usually onto the ex manifold. It's often times an annoying coolant leak that can not be traced as there is no leaking coolant apparent but because coolant is being vaporized, as it hits the ex manifold, it leaves the distinct smell of antifreeze around the engine bay.
You can fix it yourself using basic hand tools and a $1 o-ring. The process of replacing it will generally take about 1-2 hours.