I've got a 96 Grand Prix with a 3.1l that I bought used. After a week or two the pulley for the water pump fell off and the car overheated. I replaced the intake gasket, plugs, wires, o2 sensors, and cleaned out the maf. Things were great for about a week. Now if the car warms up, and I turn it off for less than 45 mins, it runs really rough and stalls out. If I try to start it again it cranks, but won't start. If I wait 45 mins it starts and runs fine. The only code that came up was p0171, lean bank 1. Does anybody have any ideas?