the butterfly can be cleaned easily without dismantling, although it's best to take the throttle body out - remove the accelerator cables, disconnect the four electrical connectors and the breather hose then remove the air intake hose then it's just the four bolts to to remove the throttle body. you can then work on it vertically. use carb cleaner to spray inside and prevent too much entering the lower throttle position sensor and the upper idle air valve as these are electrical components and could get gummed up. use a soft cloth to wipe away the goo and check the butterfly snaps (almost) shut nicely.
don't worry about gasket between the throttle body and the engine manifold -it should be clean and flat and tightened up evenly.