Idle Problems

Hey guys, I've got a question for the smart people. I noticed today that when I stop at a light, my engine idles at around 1300-1500 RPM's for a 30 seconds or so and then drops down to the normal 700-800 RPM's. I've never seen this happen before today. Is there anything I should be worried about?
'03 Tib V6 with 220,000 miles.

Thanks in advance.