What was found
SHORTLY AFTER DEPARTURE, SMOKE AND FUMES APPEARED IN THE CABIN AND COCKPIT. THE FLIGHT CREW SHUT DOWN BOTH PACKS, DECLARED AN EMERGENCY AND RETURNED TO AN UNEVENTFUL LANDING BACK AT DTW. NO MENTION OF COM COMPLIANCE. THE AIRCRAFT WAS TOWED TO THE GATE. MAINTENANCE COULD NOT FIND A POSITIVE SOURCE OF THE SMOKE BUT DID REPLACE BOTH COALESCER BAGS, THE APU, AND THE CABIN TEMPERATURE CONTROLLER. PACK BURNOUT COMPLETED AND THE LEAK CHECKS WERE GOOD SO THE AIRCRAFT WAS RETURNED TO SERVICE.