I had time, today, to look at the white Jetta. It still didn't want to start, so, I pulled the spark plugs. They were sooty and fowled with gasoline, which confirms my suspicion that the return line froze or that the fuel pressure regulator isn't working well. I used a kitchen match to burn the gas off the plugs and scraped as much soot as possible off with a bit of emery cloth. Once reinstalled, I disconnected the power to the fuel rail and turned over the engine to burn any residual gas in the cylinders. I then reconnected power to the fuel rail and upon turning over the engine the car roared to life.
I need to get a fuel pressure gauge to test the system. I suspect that the fuel pressure regulator is bad. However, I've read that this component seldom fails. The fuel pressure regulator is located at the end of the fuel rail. Inside this device is a spring-loaded diaphragm that is actuated by manifold pressure via a vacuum hose. This valve regulates fuel pressure to the injectors by allowing excess fuel to travel through the return fuel line and back to the fuel tank. If the pressure regulator fails, high fuel pressure can result causing fuel to flood the engine. This could lead to a rich mixture, observed as white smoke from the tail pipe, or, to hard starting if the pressure is excessive at initial turn over. Now, there are other possible causes. Perhaps, I have leaky fuel injectors, a vacuum problem or an intermittent obstruction in the return line. Only tests will tell. I'll get back to you once I know more.