normally a bouncing idle while the car is stationary with no change in pedal position is a vacume leak at either the intake manifold hoses or the intake manifold gasket, old crusty hoses leaking or some hose blown off somewhere or not clamped down if need be (not all hoses are clamped but some tend to fall off due to wear over time), this has been my experience with bouncing idle, high idle usually is a removed temp sensor on the back of the block causing the car to remain in warm up mode, or u need to adjust ur idle control screw on the intake manifold. hope that helps clear stuff up