I have a 1999 ml320 with a similar problem. If the car sits 30 minutes it will crank over fine and not start. 1 hour later it will start. No codes set in the computer, no spark and no fuel pressure. I have seen the problem twice and by the time I found the wires to check the crank angle sensor for alternating current the car started. I got a good signal from the sensor at 12 volts during cranking. After reading this I will replace the sensor and hope the problem will be history. John