direct fuel injection systems give the car better gas mileage and more power, however they allow carbon deposits to build up on the valves and inside the intake runners. over time this carbon will break loose in the same way that a blood clot does and it can get stuck in the valve opening not allowing the valve to close. with the valve stuck open the piston contacts it and either breaks the valve off the stem, bends the valve stem, or in the worst case, cracks the block head. to fix the problem the entire engine needs to be pulled and overhauled. basically if you are looking to buy one of these just make sure that the owner has kept up on maintenance because there are no warning signs for this issue, do this and you should have no future problems.