Hey guys, I've been searching about what can cause bad gas consumption and so forth but I still can't figure it why my car eats so much gas. I mean I understand the G35 gets like 18 mpg if you're lucky lol, but I swear I'm getting about 7 miles to the gallon.

It takes me 40 bucks to get to LA and back from Long Beach (which is not that far by the way)

I checked my tire pressure, my air filter is far from being dirty, my oil gets changed frequently, and there are no leaks from what I've inspected. There isn't any crazy smoke coming from my tailpipe, no mods, alignment is good, no sticky brakes, only extra weight is the subwoofers but that doesn't weigh much and car idles fine. I've been told by my friends I have a heavy foot, so I let my girlfriend drive for the whole day and it still ate a crapload of gas.

Although, sometimes in random occassions, I'll start my car early in the morning to warm it up and I'll get a small scent of fuel that feels like it's coming from the dash. And twice this has happened, that I haven't driven my car in about two weeks, my engine will begin to shake and feels like its idling roughly. If I shut my car off and I start it back up again, it will feel normal.

Any thoughts, ideas, or suggestions?

p.s 03 G35 Sedan with 100k miles..