While driving at around 20 mph in my neighborhood I felt like the engine was studdering. However I do notice that the V is running sluggish since filling her up today. I recently changed the plugs on Friday and everything seemed ok since then. I was running low on fuel and stopped at a gas station that was not of a known name brand. I used 93 Octane. Would the plugs cause this and if they were installed improperly would I receive a check engine light? If the fuel was actually not 93 Octane could this be the cause? If bad fuel will it hurt the motor? Thanks for the advice.