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 solenoid vent plugged or iced.
-- EGRVR circuit shorted to GND.
-- EGRVR circuit shorted to VREF.
-- Improper vacuum hose connection.
-- Plugged/pinched EGR vacuum regulator Solenoid vacuum hose.
-- Plugged EGR tube.
-- Damaged EGR vacuum regulator solenoid.
-- Pinched/iced pressure hoses.
-- Damaged differential pressure feedback EGR (D.P.F. EGR) sensor.
-- Damaged PCM.
Other than the simple things (pinched vacuum lines or electrical shorts), it looks to me that it is one of 3 things: EGR valve stuck open, DPFE sensor damaged, or EGR vacuum regulator solenoid. If you have access to a good OBD-II scanner (that can read DPFE voltage values for instance), I can give you the step by step diagnostics from the Service Manual. Otherwise, I'd start with the cheapest item first of the 3 I listed, once you have verifies that it isn't ne of the simple causes.
