Recommend that you do a search with the phrase "402". You will get lots of hits.

Basically, one of the parts of your EGR system is not working. It could be the DPFE, EVR, EGR, or PCM (and probably a few other things).

Here is the text from the Ford Technical Service Publication (TSP):

Quote:

Diagnostic Trouble Code (DTC) P0402 indicates that Self-Test has detected EGR flow at idle.

NOTE:
If DTC P1405 is in Continuous Memory, diagnose that first starting with «HE50».

Possible causes:
-- EGR valve stuck open.
-- EGR vacuum regulator (EGR V.R.) solenoid vent plugged or iced.
-- EVR circuit shorted to GND.
-- EVR circuit shorted to VREF.
-- Pinched/iced pressure hoses.
-- Improper vacuum hose connection.
-- Plugged/pinched EGR V.R. vacuum hose.
-- Plugged EGR tube.
-- Damaged EGR V.R. solenoid.
-- Damaged Differential Pressure Feedback EGR (D.P.F. EGR) sensor.
-- Damaged PCM.

1996 Contour SE Sedan 4D (Royal Blue)
Duratec V6 2.5L 24-valve DOHC
Automatic
75,000 miles
No Mods (unless you call the DMD a mod)
Replaced EGR valve (gunked up), EVR (EGR VR), PCV valve, and evaporative emissions hose (cracked).