That is the PFE, or Pressure Feedback, Exhaust sensor if it only has one hose. If it has two hoses then its a DPFE- Delta Pressure Feedback, Exhaust. The DPFE measures the difference, in pressure across an orifice in the EGR tube.
unforyunately that isnt mine mine has tools and stuff sprawled all over it still puttin the puzzle back together and i got a harmonic balencer for it so i will finnally be able to drive it later this week
The PFE/DPFE is the sensor that sends the EEC the info that indicates that there is actually flow in the EGR system. Without the indication of EGR flow the computer should illuminate the Check Engine light. The EEC may take other action, like altering timing and fuel curves, or it might not. There is still debate on this. Personal experience suggests that it does do something besides the light as I've had various cars improve their fuel economy by 1-3 mpg after getting the EGR system working (or at least to where the EEC thinks it is working.