What was found
FA REPORTS BURNING PLASTIC SMELL IN AFT ACFTDURING TAXI. ON GATE RETURN DEBRIEF CREW REPORTS ODOR IN AFT CABIN UPON #2 ENGINE START. CREW SHUT DOWN #2 ENGINE AND ODOR DISSIPATED. ACCOMPLISHED WALKAROUND EXTERNAL INSPECTION OF RAM AIR DUCTS AND BOTH ENGINES. OPERATED APU, #1 AND #2 ENGINES INDEPENDENTLY WITH BLEED AIR AND BOTH PACKS REF AMM 05-50-00-810 AND AMM 36-11-00-710. COULD NOT DUPLICATE ODOR AND NO ABNORMAL PARAMETERS. CONCURRED WITH TOMC..