How recently have you filled the tank with gas when you notice the CEL coming on?
When I first got my 3, the CEL would come on intermittently, then go off after a couple days. I went to Autozone, they told me the error code. It turns out that the fuel system is really sensitive to pressure loss due to an imperfect seal at the gas cap...now I just really crank it tight after filling up and no CELs.
I dont know if this is your issue, but it's something to consider. They may be saying "It's nothing" because they know after 40 starts that particular CEL error will self-clear...