As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER 35 MINUTES OF TAXI, LEFT THROTTLE WAS ADVANCED AND THERE WAS NO ENGINE RESPONSE. LEFT ENGINE REMAINED AT IDLE REGARDLESS OF THROTTLE POSITION. NO EICAS MESSAGE OR EEC LIGHTS DISPLAYED. ONCE APU WAS STARTED AND ELEC PWR SWAPPED CONTROL RETURNED TO LEFT THROTTLE AND ENGINE. REMOVED AND REPLACED LT ENG EEC IAW MM, OPS CKS OK. ETOPS CATEGORY 'D': INABILITY TO CTRL ENG OR GET DESIRED PWR.