Hey everybody, i have an issue with the idle on my 99 miata. When i come to a stop at anytime after my car has warmed up my idle will bounce between 2000RPM and 1500RPM. I turned my air on and it leveled out the idle to 1000rpm until i got to my parking lot at work and had to stop for a good amount of time to wait on a spot and it started doing the same thing and the air got very hot. Any idea on what it might be?

Thanks everyone