1997 Cadillac Concours diagnostic trouble code P1660

My service engine soon light has been on for about three days, here are some of the malfunctions that I have noticed, (1) I usually use 93 octane but I recently used 87 octane due to the high price of fuel maybe this can be a factor. Im currently due for an emmission inspection. (2) temperature tends to rise slightly in stop and go traffic or when sitting idle at stop light. (3) brake lights have a tendency to engage automatically sometimes while driving, when this happens the cruise control will dissengage, I have to pull over and repeatedly press the brakes to make the light go off. (4) usually when I shift to drive or reverse my emergency brake will release automatically, here lately it will noy release on its own, I have to manually release it with the secondary parking brake release leveler. My on dash screen displays these two items, (1) vehicle will not exceed speeds over 90 mph (2) vehicle speed. Any one who can tell me the correct things to do to correct these issues will be compensated if your hypothesis works, call tek at 678-698-8152 anytime, thanks