Narrative:

I was in a cessna 172E at 6000 ft MSL when I encountered engine roughness. My initial reaction was to put the mixture rich because the fuel flow gauge kept fluctuating showing 4-6 gph. I was running on the right fuel tank at the time and switched to both tanks. I kept troubleshooting to avoid the engine from running rough. I intermittently switched the electric fuel pump on and off which smoothed out the engine for a short time. I eventually turned the fuel pump off because I didn't want to burn the pump out. ATC knew I was having engine roughness prior to approaching the VOR. After about 30 mins of trying to keep the engine from running rough; I requested to be diverted to ZZZ2. A few mins passed by and no answer from ATC. I then requested to be diverted to ZZZ3 since it was the next closest to me at the time. A few mins passed and still no answer. I kept on with my request to be diverted until ATC told me to turn around towards ZZZ and land. They (ATC) were going to declare an emergency. I complied and was vectored to landing. During the descent; the engine kept running rough until touchdown. After landing and during taxi; the engine operated normally. I was taxied to and shut down at the GA terminal at ZZZ. I flew home via commercial carrier and the aircraft was picked up by a mechanic and another pilot several days later. Cause of engine roughness is still unknown. An investigation is still underway.

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Original NASA ASRS Text

Title: C172 PLT SUFFERS ROUGH RUNNING ENGINE AND REQUESTS LNDG AT THREE AREA ARPTS. EMERGENCY IS DECLARED AND A SAFE APCH AND LNDG RESULT.

Narrative: I WAS IN A CESSNA 172E AT 6000 FT MSL WHEN I ENCOUNTERED ENG ROUGHNESS. MY INITIAL REACTION WAS TO PUT THE MIXTURE RICH BECAUSE THE FUEL FLOW GAUGE KEPT FLUCTUATING SHOWING 4-6 GPH. I WAS RUNNING ON THE R FUEL TANK AT THE TIME AND SWITCHED TO BOTH TANKS. I KEPT TROUBLESHOOTING TO AVOID THE ENG FROM RUNNING ROUGH. I INTERMITTENTLY SWITCHED THE ELECTRIC FUEL PUMP ON AND OFF WHICH SMOOTHED OUT THE ENG FOR A SHORT TIME. I EVENTUALLY TURNED THE FUEL PUMP OFF BECAUSE I DIDN'T WANT TO BURN THE PUMP OUT. ATC KNEW I WAS HAVING ENG ROUGHNESS PRIOR TO APCHING THE VOR. AFTER ABOUT 30 MINS OF TRYING TO KEEP THE ENG FROM RUNNING ROUGH; I REQUESTED TO BE DIVERTED TO ZZZ2. A FEW MINS PASSED BY AND NO ANSWER FROM ATC. I THEN REQUESTED TO BE DIVERTED TO ZZZ3 SINCE IT WAS THE NEXT CLOSEST TO ME AT THE TIME. A FEW MINS PASSED AND STILL NO ANSWER. I KEPT ON WITH MY REQUEST TO BE DIVERTED UNTIL ATC TOLD ME TO TURN AROUND TOWARDS ZZZ AND LAND. THEY (ATC) WERE GOING TO DECLARE AN EMER. I COMPLIED AND WAS VECTORED TO LNDG. DURING THE DSCNT; THE ENG KEPT RUNNING ROUGH UNTIL TOUCHDOWN. AFTER LNDG AND DURING TAXI; THE ENG OPERATED NORMALLY. I WAS TAXIED TO AND SHUT DOWN AT THE GA TERMINAL AT ZZZ. I FLEW HOME VIA COMMERCIAL CARRIER AND THE ACFT WAS PICKED UP BY A MECH AND ANOTHER PLT SEVERAL DAYS LATER. CAUSE OF ENG ROUGHNESS IS STILL UNKNOWN. AN INVESTIGATION IS STILL UNDERWAY.

Data retrieved from NASA's ASRS site as of May 2009 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.