What was found
AFTER TAKE OFF, PASSING 1500 FT. RECEIVED AURAL TRI-TONE FOR NR 2 MANIFOLD FAIL, CHECKED AIR SYS SYNOPTIC VERIFIED, REDUCED POWER TO IDLE NO HELP, STILL RED MANIFOLD INDICATIONS. RED TABS ACCOMPLISHED, RETURNED TO DEPARTURE. R & R VALVE IAW AMM 21-41-15-4, LEAK AND OPS CHECKED GOOD. PERFORMED DECAY CHECK AND NOW PASSES AT 21 SECONDS. REF FOR SECOND TEST. REMOVED MEL AND RESET MANIFOLD FAIL SYS TO NORMAL OPERATION AND COMPLETED AN AIR SYS TEST WITH NO FAULTS. FINAL CLOSED.