Hello,

2007 GD3, manual transmission. No mods except HFP muffler.

so my scan gauge is bringing up p0457 evap leak (pending code) and my dashboard is showing check fuel cap. Got the message on the highway so I took an exit, pulled over and tightened the cap. Still the code. Stopped the car, cleared the code, tightened the cap and went on my merry way. Code and dash warning came back on while driving on the highway. Tried tightening and restarting today (24h later) and still same. Idling a little rough too.

I don't see any obvious loose airbox hoses but I checked my air filter and it is pretty dirty (yes yes, I will change it ASAP). Could it be a dirty air filter is the culprit? My gas cap gasket looks nice and clean and the fuel line opening is clear of debris.

Any suggestions?

 

substitute gas cap and recheck
Gas cap has a vacuum valve (can be stuck open) and filler neck seal which either cracks or hardens allowing leaks. Most smog shops checking the gas cap but this "checking" cost more than a new or used cap