PO420 Code

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Check engine light came on at 116,800 miles. Had it checked and it was PO420. Took off bank two oxygen sensor and not really carboned. Took off PCV and it was clogged. Cleaned it out (rattle now heard) disconnected the battery and reset the PCM. Engine light has not returned. Went to move the van to a flat area to change the oil (two minutes of run time), and van would not stay started. Had to give it a "little" pedal, not floored. When van reached running temp. it ran fine and even re-started fine. Had several days of great starts and then the "low idle" stalling issue returned. IAC need cleaning? Throttle Body Cleaning? VSV issue? Help....