P0402 does not indicate a need for TB cleaning, that is a P0401.
Here is the first step of the P0402 diagnostic:
"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.
l Disconnect vacuum hose at EGR valve and plug hose.
l Run Key On Engine Running (KOER) Self-Test.
l Key off.
l Was KOER DTC P0402 output or unable to run KOER Self-Test due to engine stall or no start?
Yes
There is possible EGR flow at idle. INSPECT pressure hoses first for pinching and icing. If OK, REMOVE and INSPECT the EGR valve and EGR tube for signs of contamination, unusual wear, carbon deposits, binding and other damage. REPAIR as necessary. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN «Quick Test».
No
RECONNECT vacuum hose to EGR valve. GO to «HE21»."
My initial guess of the most likely faults would be either an EGR valve that is not fully closing or is leaking or you have a faulty DPFE sensor.
Steve
