RPM needle under 1?

I got 2003 automatic toyota celica with 122000 miles. My question is why does or what does it means when my RPM needle stays between 0 and 1 marker? When I come to complete stop on red light on "drive", the needle stays betweeen 1 and 0 maker and idles little or barely little bit. To avoid that, I would usually put it in "nuetral" and my car would feel "smooth". Now like recently, I notice the RPM needle stays between 1 and 0 regardless I put the car on "drive" or "nuetral" option. Any advice I should take? Thanks :)