Q: my heat gauge goes up when idling then comes back down when driving

It sounds as though you are probably having an issue with the cooling fan(s). The primary function for the cooling fan(s) is to push/pull air through the radiator at low speeds, or at a stand still. When stationary, there is not sufficient air flow through the radiator to cool the liquid in the cooling system and keep the engine at the proper temperature. There could be a problem with a clogged radiator, but this issue would normally be observed whether stationary or moving. Without knowing the model of the vehicle, and the engine it is equipped with, I don’t know if it is a belt driven cooling fan, if it is electric, or if it is mechanically driven. In any event, I would have the function of the cooling fan diagnosed. If this is something that you feel you could use a hand to diagnose and/or repair, contact a certified mechanic, like those available at YourMechanic.com.