What is this?

[floatingpig]

Hi guys,
I was working on replacing my spark plugs and wires today when I noticed this on my engine. I assume it's not supposed to be melted away like this. A few questions about it:
1) what is it, what does it do?
2) how did it get in that condition?
3) do I need to replace it urgently?
4) what's the part number?

I'm at around 152k miles on my 2000 Explorer 4.0l SOHC, it runs fine (maybe idles a little rough). I'm doing a few things for perventive maintenance like spark plugs, fuel filter, etc.

 

[swshawaii]

DPFE Sensor

http://www.explorerforum.com/forums/showthread.php?t=164517

 

[2000StreetRod]

melted DPFE sensor

That often happens when one of the hoses comes loose and exhaust flows up to the sensor.

 

[drdoom]

Replace it, and the hose get some emissions hose.