[mjc3276]

Thank yall for the guidance. I think I got it fixed. I had a P0305 code come up (as well as P0449 and P0455). That helped really hone in the issue as I went to put in a new plug, the stupid spark plug wire was off my #5 cylinder. Cleared the codes and put a 40 min ride on her... shes been behaving. The P0171 and P0174 were cleared as I got a new gas cap.

I do expect to have to change the canister and purge valve... I hear they are a common issue.

 

[mjc3276]

I got the same thing on my 2009 Sierra, same codes and fuel cap message. It was the fuel tank pressure selanoid and hose that I had to replace. It effects the pressure in the fuel tank and results inbad fuel mileage.

whereis it located and... do I need to drop the tank? that make sense why im haveing hard starts only after just filling up. this is a recent phenomenon.

 

[mjc3276]

I had the same problem, and 496 keeps popping up. The rough idle still exists especially when under 45 degrees F at first start. Part of the issue was a loose spark plug wire. I fixed my purge vacuum issue (lines) but STILL hear a leak. I have a fog machine coming to smoke it out. Im thinking its either a bad seal on intake or valve cover (which dealer replaced 3 months ago when I showed them an AFM bulletin from the Forum).