It's the weirdest thing, my service engine soon light comes on and then a few days later it shuts off. This has been happening for the last 3 months. I had it checked and I was told that I need a new EVAP valve. My question is, why the light would shut off if there is a problem? If there truly is a problem wouldn't the light stay on all the time?I was also tolod that I got a K/S sensor code, but I know that won't trip the C/E light.

 

If the problem comes up and then goes away, the CEL will turn off after 50 starts. But, the code is still stored. Learn to check your own codes. If you ask how here, however, you will be banned.