2000 Windstar Surging?

I have a 2000 with 86000 miles on it. Recently the engine seems to run a little more rough than it used to. Its more like more vibration than anything. Also it seems to be surging slightly, no bucking and no rpm fluctuation but you can feel it. Seems to accelerate fine and start easily. I am changing the plugs and fuel filter this week. Has anyone else experienced anything like this? Thanks

Have you had the upper manifold gaskets replaced yet? Check for vacuum leaks around manifold. Also checked for sticky idle air control valve or coked up throttle body.

Problem has been solved. Noticed drum was hot to the touch. Found left rear wheel cylinder was frozen. Replaced shoes and cylinder and all is well!:)