Lately (mostly during hot days) I've noticed I get a rough start out of first. I would guess plugs, but my idle is fine. Its only out of first (and sometimes on a downshift) that I get a brief period of engine strain as I move up past the lower rpms. Once I get going I don't notice it. On cooler days this is not as noticable, but there is a fuel smell that almost takes the place of the rough start. Could this be the O2 sensor?