I know this is a different motor but I had the same exact thing happen on my 3.0 VW diesel last week. Started fine when cold, when warm would only crank, no fire. Let it cool down again, started just fine. Put a good scanner on the car, read some codes, looked at some real time data. Turned out to be a cam position sensor went bad. $46.46 and 6 minutes later, all done.