Narrative:

We were at 13000 ft on an IFR flight plan from eau to vay. We had been cleared direct erie. South of flint, mi, the left engine began to experience a fluctuation in fuel flow. Within mins, the left engine began to fluctuate between 2100 and 2500 RPM's (cruise setting). I first advised ATC of a rough running engine. They were very helpful. I then decided to retard the left engine to zero thrust (12 inches manifold pressure) because I had good oil temperature and pressure on the left engine. ATC cleared me to 12000 ft and advised that selfridge was 12 O'clock and 5 mi. I requested a different airport. ATC advised detroit metropolitan was 40 mi, but detroit city was 8 mi. I descended to 12000 ft, but may have gone lower without ATC clearance. I was eventually cleared to the field. ATC was very helpful. I landed without further incident. No damage to the aircraft except an intake valve on the #2 cylinder on the left engine. The engine had given me difficulty in starting on the last 3 flts. After each start, I would do multiple run-ups and would run the engine at idle without a problem. I should've had a mechanic thoroughly inspect the engine regardless.

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Original NASA ASRS Text

Title: AN SMT PLT EXPERIENCES A LOSS OF PWR ON THE L ENG AND DECIDES TO DIVERT TO AN ENRTE ARPT. THE INTAKE VALVE IN THE #2 CYLINDER ON THE L ENG WAS FOUND TO BE DAMAGED.

Narrative: WE WERE AT 13000 FT ON AN IFR FLT PLAN FROM EAU TO VAY. WE HAD BEEN CLRED DIRECT ERIE. S OF FLINT, MI, THE L ENG BEGAN TO EXPERIENCE A FLUCTUATION IN FUEL FLOW. WITHIN MINS, THE L ENG BEGAN TO FLUCTUATE BTWN 2100 AND 2500 RPM'S (CRUISE SETTING). I FIRST ADVISED ATC OF A ROUGH RUNNING ENG. THEY WERE VERY HELPFUL. I THEN DECIDED TO RETARD THE L ENG TO ZERO THRUST (12 INCHES MANIFOLD PRESSURE) BECAUSE I HAD GOOD OIL TEMP AND PRESSURE ON THE L ENG. ATC CLRED ME TO 12000 FT AND ADVISED THAT SELFRIDGE WAS 12 O'CLOCK AND 5 MI. I REQUESTED A DIFFERENT ARPT. ATC ADVISED DETROIT METRO WAS 40 MI, BUT DETROIT CITY WAS 8 MI. I DSNDED TO 12000 FT, BUT MAY HAVE GONE LOWER WITHOUT ATC CLRNC. I WAS EVENTUALLY CLRED TO THE FIELD. ATC WAS VERY HELPFUL. I LANDED WITHOUT FURTHER INCIDENT. NO DAMAGE TO THE ACFT EXCEPT AN INTAKE VALVE ON THE #2 CYLINDER ON THE L ENG. THE ENG HAD GIVEN ME DIFFICULTY IN STARTING ON THE LAST 3 FLTS. AFTER EACH START, I WOULD DO MULTIPLE RUN-UPS AND WOULD RUN THE ENG AT IDLE WITHOUT A PROB. I SHOULD'VE HAD A MECH THOROUGHLY INSPECT THE ENG REGARDLESS.

Data retrieved from NASA's ASRS site as of July 2007 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.