What was found
MCI - FLIGHT ATTENDANT REPORTED ON CLIMBOUT WHOOSHING AT AIR/CYCLING VALVE APPROXIMATELY EVERY 15 SECONDS AT SAME TIME STRONG FUMES AND SMOKE IN CABIN AND COCKPIT. APU WAS SHUTDOWN AND SMOKE INITIALLY CLEARED BUT STARTED BACK UP AGAIN AFTER 1 MINUTE. EMERGENCY DECLARED RETURNED MCI LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. ACCOMPLISHED AUXILIARY POWER UNIT INLET DOOR WASH CARD 49-97-12 AND APU WASH PROCEDURE 49-97-11. ACCOMPLISHED PACK BURNOUT PER CARD 21-92-12. SYSTEM GROUND CHECK NORMAL OPERATION.