when you look inside the tb when its on the car it looks all clean, but if you open the butterfly, all the carbon is behind the flap. you can clean it while on the car, but its a better job if its off. you can use some tb cleaner, and a tooth brush to get past the flap, and the back side of the flap, then use a rag on the tooth brush to clean it all up.
and dont mess up the screen on the out side of the tb, there is a spring clip around the out side holding it in, 2 picks will let you pop it up and out so the screen comes out.
