What was found
AIRCRAFT WAS GNDED. NR 2 ENG STALLS. FIVE HRS INTO FLT, HAD BEEN AT FL400, REC MAX 409 FOR ABOUT 5 MIN WITH NO TURB & GOT NUMEROUS NR 2 ENG STALL ECAM WARNINGS. ENG WOULD GO TO IDLE, ECAM WARNING WOULD DISAPPEAR & ENG WOULD ACCELERATE TRIGGERING THE WARNING AGAIN.. ACCOMPLISHED ENG STALL, NOT DISPLAYED ON ECAM, QRH PROCEDURE WHILE DESCENDING TO FL300. AT FL300 BOTH ENG INDICATIONS WERE NORMAL & STABLE. CONTINUED & REPLACED THE NR 2 ENG FUEL PUMP, FUEL DIFFERENTIAL PRESS SWITCH & FUEL METERING UNIT IAW AMM 73-11-11 & 73-21-12. THE NR 2 ENG L & RT 8TH STAGE CHECK VLVS WERE FOUND TO BE FAULTY & WERE REPLACED IAW AMM 36-11-41. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.