multigrid for numerical solution of 2d euler equa

jim

I AM PRESENTLY TRYING TO ACCELERATE THE CONVERGENCE OF MY FLOSOLVER using multigrid. I get a fairly good early acceleration for the first classic v-cycles; however afterwards, when shifting to the fine grid (prolongation using simple averaging), I start getting oscillations that become progressively large until the residue fall saturates before reaching convergence. Can anyone tell me how to avoid the problem and how to prolong the data from coarse to inorder to avoid those oscillations. I am using a finite difference based code. thanks Jim