PLT OF A PIPER PA24 COMMANCHE DIVERTED TO LAND DURING AN IFR FLT DUE TO A ROUGH RUNNING ENG. CARB ICE WAS SUSPECTED.

Narrative

DURING CRUISE FLT AT 9000 FT MSL FROM WADSWORTH; OH (3G3); TO COLLEGE PARK; MD (CGS); THE ENG BEGAN RUNNING ROUGH; ALL OF THE SUDDEN. THE PLANE WAS SHAKING FROM THE ROUGHNESS AND I HAD JUST CHANGED ZOB SECTORS. ON RPTING ON; I ADVISED AT 9000 FT AND REQUESTED TO LAND MORGANTOWN; WV (MGW). A CHK OF THE CHARTS AND LORAN VERIFIED MGW AS 10.4 MI AWAY. I TRIED TO CLR THE ENG AND IT STILL RAN ROUGH. CARB HEAT WAS ADDED; THE PROP WAS SET TO HIGH RPM. TO AVOID ANY FURTHER POTENTIAL DAMAGE TO THE ENG OR AIRFRAME; I DECIDED ON A PRECAUTIONARY LNDG WITH MINIMAL PWR. CTR GAVE A VECTOR TO THE ARPT AND XFERRED ME TO CLARKSBURG APCH WHO CONFIRMED THE SIT AND REAFFIRMED A VECTOR AND LOWER ALT. I ARRIVED OVER THE FIELD WITH 4000 FT AGL; WAS GIVEN PRIORITY AT THE FIELD BY THE TWR AND LANDED WITHOUT INCIDENT AFTER A VERY CLOSE PATTERN. INSPECTION ON THE GND REVEALED NO AIRFRAME OR ENG PROBS. I REFILED THE IFR FLT PLAN AND CONTINUED ON TO CGS. I CAN ONLY SPECULATE THAT CARB ICE HAD FORMED AND DISLODGED CAUSING THE ROUGHNESS; NO OTHER CAUSE HAS BEEN FOUND.