Ok so first let me explain what it is doing and what I have changed on this vehicle. My van is making a squealing noise when it gets louder it will jerk and try to turn off also it has turned off on me. I have gotten the serpentine belt, alternator, tensioner, idler pulley, and battery changed. After I got it fixed it stopped that day and now its back to making these noises again. What do I need to look into now? My CEL is on and I got the codes P0171 and P0174. I dont know what else to do and how much more I can afford on this thing. Please help.