For the last few days I get a message on the DIC saying tighten fuel cap. I appears breifly then goes away.I checked the fuel cap and it is tight. Anybody have any ideas what this could be? I have a bad knock sensor that I'm going to try and replace next week could this be related?

 

You have a small evap leak that disappears shortly after your EVAP monitor runs. Have a mechanic look for the leak, you might just need to replace your fuel cap.

 

I agree replacing the fuel cap may fix the problem.