What will cause the car to idle rough and have no horse power ?

A vacuum leak could be the cause. How many miles and what kind of maint.? Check engine light on?

While a vacuum leak can cause a rough idle, it will not usually cause a drop in hp. I would be leaning more to a stuck open EGR valve. At any rate, you should have an engine light on. Try to get the codes pulled so you have a direction to go.