If, in fact, your throttle is either on or off with the left stick (not proportional) the way to control altitude is by "blipping" the throttle stick, in other words, once you climb to altitude, momentarily let go of the throttle, then apply throttle as it starts to descend. You will find a rythm of on-off throttle modulation that will let you keep the plane at the height you want. Same goes for turns--if you want to turn right, don't hold the stick over to the right, but "blip" it at a rate that gives the turn you want. Holding a turn input with this type of plane can often result in a spiral dive (not good). By the way, the dipping you refer to could possibly have been several things--the two that readily come to mind are: a small gust of wind, or radio interference. Wind you can't do much with, but avoid. Radio interference could have momentarily stopped the motors, causing the dips--on this plane, there may not be a whole lot you can do to avoid interference, but to cope with it, you may wish to keep the plane relatively low and close, to reduce the chance of a "flyaway" (when the plane essentially stops listening to radio commands and goes on merrily about its business).