Well... ambient should be around 80 on the cool side, 90 on the hot spot. I know it can be difficult to keep up sometimes. You should not let those ambient air temps drop below 75F though! Especially if it is humid in the tank. Humidity + low temps = RI.

What is your set up like? Temps, thermometers, thermostats, caging, heat source(s)?

I also wonder if it's possible that your snake already had an RI brewing before you got her/him?