What was found
UPON ROTATION, A STRONG ACID ODOR BECAME EVIDENT IN COCKPIT. CABIN CREW ALSO NOTED THE SAME ODOR IN THE PASSENGER CABIN AREA. COCKPIT CREW DECLARED AN EMERGENCY AND MADE AN UNEVENTFUL OVERWEIGHT LANDING. MAINTENANCE PERFORMED MULTIPLE MAINTENANCE CHECKS INCLUDING ENGINE RUN, PACK CHECKS, OIL CONTAMINANTS, AND OVEN CHECKS/REPLACEMENT WITH NO CONCLUSIVE DISCREPANCIES. AIRCRAFT RETURNED TO SERVICE.