I am embarrassed to admit that I've been chasing this problem for two solid weeks. I thought I'd post the results on the chance someone else might save some time.

Vehicle: 2002 Ford Explorer EB 4.6LV8

Symptom: Sudden incidence, cranks fine, doesn't start, doesn't set any codes

Inspected and tested, no problem found: fuel tank, fuel pump, fuel filter, crank position sensor, fuel pressure, MAP sensor.

Problem found: Black goo blocking Idle Air Control solenoid valve. The valve is supposed to be open a little bit all the time, and opens farther as the ecu pulses it for more idle air. The engine was getting _no_ air, so it wouldn't start.

Symptom allowing diagnosis: It _would_ start if the throttle was held half open during cranking; it just wouldn't idle. It's been years since I've owned a carbureted car, so I didn't even try opening the throttle until today.

Corrective action: Filled the valve interior with Brakleen and cycled the solenoid with 12V a few dozen times. After the first cycle, the Brakleen started draining out, so I kept flushing until it came out clean, and reinstalled the same valve. Luck was with me; the gasket remained intact, so I didn't even have to replace that.