I recently had my radiator replaced in my 2003 Mazda 6. After picking it up from the mechanic, I noticed that the engine will idle anywhere between 1500-2000 rpm (depending on how warm the car is) when I drop the car into neutral while coasting (manual transmission). The car idles perfectly while stopped. Is this supposed to happen? I'm asking because I didn't notice this before, but my radiator was clogged (previous owner used stop leak).