I have a 2004 deville stalling at idle. I had trouble getting the car to start and had to give it some gas, and it would stall when I stopped. I cleaned the throttle body so far, with no help. I was going to clean the idle air control valve next. The check engine light came on recently so I just pulled the codes. Here is what I've got. P0121 throttle position sensor. P0300. Cylinder misfire. P0335. Crankshaft position sensor. P0455 evap leak. P507 idle speed high or low. P1372 crankshaft position sensor a-b correlation. I also just got a check gas cap message I don't know if that would cause the p0455 code. The auto zone guy suggested to start with the crankshaft position sensors and that they could cause stalling. Any suggestions? If I replace the crankshaft position sensors there are two of them at least according to autozone replace them both?