Ok so I have had my 08 g37s 6mt for about 4 yrs now. Its been a phenomenal car to own but recently its been acting up. It feels fine when it first starts going. Idle sits at 700, then after i drive it on the freeway to work when i come to a stoplight its idling at 900 and wont go down. It also has a noticeable lack of power. Its like when its cold its fine but after its warmed up its limping. No cel lights. Ive done ecu reset and idle relearn an it still does this. I have no idea what it could be. The only mods i have are k&n drop ins, smooth elbow intake tubes an a axle back. This just started happening out of nowhere...please help!!!

 

Throttle bodies likely need a good cleaning and relearning. See @MotorvateDIY on YouTube.