I have a 2007 DTS that was overheating. I had the water pump replaced, 2 gaskets and a new belt put on the car. When I went to pick it up it would not start. I kept turning it and I heard sound, but nothing. The mechanic came out and after a few times of trying to start the car it started. Now the car dies when its idle or just really hard to start. Would anyone know what could be going on? The mechanic keeps checking the wires to see what is wrong, but they can't find the issue. I was told that when replacing the water pump they had to get to the engine to do so and maybe a wire got damaged. They can't find what is wrong. Could anyone tell what the problem could be?