Went to start my 2012 Accord 2.4 with 43K miles and it spun over fine then stumbled and died, it never really completely fired up though on the first try. Second try it spun over then stumbled for a second or two before firing up. This happened after sitting for 3.5 hours after the last drive. It has done the stumble before starting thing before, but its never taken two tries to start. I started it back up 1 hour after this episode and it fired up fine. What would cause this stumble / hard start? I only use Shell (top tier), and the car is maintained to the n'th degree. The battery is less than 1 year old by the way.