Yes, replace the cooler, 70c+ is far too high for an idle system. It should be closer to 40-45c when idle or less. Vic 40already recommended that you change your cooler. You might still be able to buy the Deepcool GAMMAXX 400 from newegg for $17-18 with promo code if you are a US customer. https://www.newegg.com/p/N82E16835856005
Clapback - 70 DegC is extremely hot for idle temperatures. In the interim, you may want to recheck your CPU cooler installation. Did you properly apply the thermal paste/compound, and is the cooler firmly attached on all sides?