My 2006 S60 2.5T Has had a good history of quickly starting up at a turn of the key. Within the past 2 - 3 weeks, every once in a while (once or twice a week) when I try to start a warm engine, it turns, begins to fire, then sputters out. When I try to restart in immediately, it starts normally. Any suggestions? We have had record breaking heat (98 - 104 degrees) and my A/C is getting a workout. Many thanks