Remove your air cleaner filter element and look inside your throttle body with a flashlight, If you see any black gunk in there it probally just needs cleaning, sometimes too much oil in the crankcase can cause this problem as it gets sucked through the breather and into the throttle body, it makes a dirty mess. To clean the inside go to your local auto parts store and get some automotive throttle body cleaner in a spray can follow directions on the can, and when you are cleaning it clean the IAC plunger through the small hole in the inside of the top of the T/B, this gets dirty and will make the engine surge. Hope this helps.