From Longman Dictionary of Contemporary Englishthrottle back phrasal verbTTCto reduce the amount of fuel flowing into an engine, in order to reduce its speed → throttle→ See Verb table
Examples from the Corpus
throttle back• During this time the main engines gradually throttle back.• I tried to pull the canopy back but it was impossible against the dive so I flattened out and throttled back.• A boat's engine, throttled back and purring softly, somewhere beyond the headland to the east.• Weight was slowly ebbing; the rockets were being throttled back as the ship eased itself into orbit.• When throttling back select carburettor heat before doing so. 