Small Transport
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Departure Airport
Aircraft
Level at 11;000 feet MSL in cruise for about 2 min when CAS (Crew Alerting System) alert sounded and left MAP (Manifold Absolute Pressure) went to 58'. Props remained at cruise setting.  CAS messages were 'Hi MAP and Hi fuel pressure'.  I reduced the left throttle lever to stabilize the engine to about 70% power which brought the lever to 60% or more towards idle. I descended to 7;000 feet to see if engine would stabilize back to normal without success.  I then returned to ZZZ. The throttles remained split until landing where they matched at idle with both engines at idle. Returned passengers to the gate. None of passengers seemed distraught or concerned.
Pilot reported engine malfunction occurred during cruise flight that resulted in an air turn back.