2006 Tiburon Engine

Hey guys i fixed a 2.0 liter engine for a friend that bend a connecting rod and changed bearing, the problem is that the car idled great on the first start went for a drive up and down hills and no problem. The thing was when we drove on straight flat road the car went off and did not start. When it starts, you can not accelerate because it turns off or starts to bog. What can this be? I need your help!!