As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT ENGINE PNEUMATIC SUPPLY PULSES TO 0 PSI ON THROTTLE RETARD THEN CATCHES UP. PRESSURIZATION OK BUT PULSES ALSO. REPLACED LT ENG HP S/O VLV PER MM. REPLACED HP CONTROLLER. NDS CK OUT. NO HELP. REPLACED LT ENG BLEED AIR CARD AND PRV CONTROLLER PER MM. CKS NORMAL. REMOVED MCO/PLAC.