Anyone have any ideas what is causing this at idle? Already replaced the iac valve. This is a 2003 5 speed manual coupe. Threw a P0507 code and the car is catless if that matters, also when i drive it and go to shift while its doing that bouncing the rpms drop drastically when i push in the clutch to shift it is not the normal gradual fall. I cleaned the entire throttle body when the issue first arose, but it persisted, so I replaced the throttle body gasket and the iac valve. However, not only did the issue recur, it got worse. Initially, it was just sporadic surges while idling, but now it happens whenever I am in neutral idling for a short while, but it will go away when I restart the car. I haven't tested this thoroughly, but it doesn't appear to occur when I am in gear stopped.