PA31 pilot reported an engine malfunction in cruise resulted in a diversion.

Attributes
ACN	1612237
Time
Date	201901
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	PA-31T Cheyenne I
Operating Under FAR Part	Part 135
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Engine
Person 1
Function	Single Pilot Captain Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 5000 Flight Crew Type 500
Events
Anomaly	Aircraft Equipment Problem Less Severe

Narrative:

1. Sudden lurch; identification'd problem engine (left)2. Checked power; left engine remained stable at 25' mp3. Contacted center (problem occurred just as tower switched me to center); advised them of engine trouble. I did not declare an emergency; as the engine was stable; and the oil pressure was in the green.4. Worked on adjusting right engine to maintain altitude. 5. Continued to correct heading while navigating to VFR conditions; read gauges; troubleshoot. Referred to checklists and company procedures.6. Noticed considerable oil running down the wing; immediately [coordinated with] center; and diverted to ZZZ.7. Landed without incident.

Original NASA ASRS Text

Title: PA31 pilot reported an engine malfunction in cruise resulted in a diversion.

Narrative: 1. Sudden lurch; ID'd problem engine (left)2. Checked power; left engine remained stable at 25' mp3. Contacted Center (problem occurred just as Tower switched me to Center); advised them of engine trouble. I did not declare an emergency; as the engine was stable; and the oil pressure was in the green.4. Worked on adjusting right engine to maintain altitude. 5. Continued to correct heading while navigating to VFR conditions; read gauges; troubleshoot. Referred to checklists and company procedures.6. Noticed considerable oil running down the wing; immediately [coordinated with] Center; and diverted to ZZZ.7. Landed without incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.