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2004 corolla ce, 95,000 miles . all original O2 sensors,etc.,etc. cel light was on. i disconnected the battery and cleaned the maf with the special maf spray . light went off ,but returned a few days later. then i went to advance auto parts for a scan. they said could not read scan code, but says the car has a leak in the emissions system. (???) they cleared the cel light and it has not returned. what would " emissions leak" be all about?