What was found
ENROUTE AT FL300, NR 1 ENG EGT INDICATED TEMPS BETWEEN 027 & -046 DEGREES C. CREW REPORTS READINGS TO BE NORMAL AT START UP & ASCEND. DURING CRUISE NR 1 ENG EGT DECLINED FROM 300 TO -34 WITHIN 5 MINS, STAYED AROUND -34 DURING ENTIRE CRUISE (AROUND THE SAME TEMP AS THE OAT). AT DESCEND, EGT VALUE WENT BACK TO NORMAL, THEN ENG 1 SHOWED 80 HIGHER THAN ENG 2 ON GROUND. CREW CYCLED ANTI-ICE SWITCH WITH NO LUCK. ALL OTHER PARAMETERS READ NORMAL. FADEC DID NOT SHOW ANY LAST LEG FAULTS, REF TSM 77-20-00-810-801-B FOR FURTHER T/S. REPLACED DAMAGED LOWER OTBD NR 4 EGT PROBE, OPS CHECKED GOOD IAW AMM 77-21-15/401, CONFIG 13.