My Q7 is having the same issue. Runs fine. Sometimes refuses to start (this has happened only when engine is still hot). Engine cranks for about 2 seconds and stops (no firing at all). It's not the starter motor as cranking speed is very good. This has started to happen after replacing my battery (could be a coincidence). Also, I've noticed that the led in the door doesn't flash when you lock it through the fob (it remains solid red). The car, however starts if you leave it for 15 minutes.
Could it be something related to immobiliser? Did you manage to solve the issue in your Q7?
