[RIP]

How old are the spark plug wires, plugs and air filter? Was any maintenance done just prior to this starting? Backfiring out the intake indicates a lean condition. Out the exhaust indicates a rich condition. Which is yours? Any experience using a multimeter? First thing I would do is check the coil, spark plug, and cam/crank sensor and TPS connections for anything amis. Look for corrosion or contact damage. You could try disconnecting each spark plug wire one at a time. The one that doesn't change the idle is the one not firing, if any. An easier way to check for spark is to connect a timing light to each wire and look for the one not producing a flash. Next connect a fuel pressure gauge at the fuel rail test port and see what pressure the pump is producing. Better to check it when it's running rough. Look for a steady 49 psi. An Autozone or the like can lend you a gauge. Have them scan for codes. It's free. If all looks good clean the EGR valve and vacuum lines, though I would have doubts it would keep you from starting. Still bad with no code? Change the cam and crank sensors.

I'll never say never but the fuel filter has filtering capacity to spare. It's designed to last the life of the van. Not a likely culprit.