HDG DEV OFF COURSE; THEN VIBRATION FROM ENG. PRECAUTIONARY LNDG.

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DEPARTED N54 (LANGHORNE; PA) ON IFR FLT PLAN TO ALB. WAS INSTRUCTED BY PHL APCH TO CLB TO 6000 FT DIRECT ALLENTOWN. I GOT ON THE 157 DEG RADIAL (337 HDG) AND LOCKED ON AUTOPLT. ACFT SHORTLY THEREAFTER (STILL IN CLB) STARTED TURNING TO R. HOWEVER; VOR NEEDLE STAYED CENTERED. I TUNED SECOND VOR AND GOT SAME RESULTS. BY THE TIME I GOT TO 030 DEG HDG I KNEW SOMETHING WAS WRONG BUT THE NEEDLES WERE STILL CENTERED. AT THAT TIME PHL APCH ASKED MY HDG. I RESPONDED THAT I WAS ON 337 RADIAL OF ALLENTOWN (DOUBLE WRONG ANSWER -- I WAS ON 157 RADIAL AND HE ASKED HDG). CTLR (ANGRILY) RESPONDED -- ANSWER MY QUESTION! SAY HDG. I SAID 010 DEG (I HAD TURNED BACK; VOR NEEDLES WERE NOW SHOWING R OF COURSE). HE SAID I HAD TURNED AWAY FROM ALLENTOWN AND 'FLY HDG 330 DEG' WHICH I DID. VOR REFLECTED MAX OF 3 DOTS DEV. I HAVE NOT BEEN ABLE TO DUPLICATE THIS PROBLEM ON SUBSEQUENT FLTS. I ATTRIBUTE IT TO AUTOPLT ANOMALY. VIGILANCE OF INSTS IS IMPORTANT AT ALL TIMES. I PROBABLY WAS 30 SECONDS - 1 MIN SLOW IN CORRECTING THE HDG DUE TO CONFLICT OF READINGS. A FEW MINS LATER; HAVING BEEN HANDED OFF TO ALLENTOWN APCH AND CLRED FROM 6000 TO 7000 FT MY ENG GOT A SUDDEN VIBRATION. MY ENG INSTS WERE NOT SHOWING A PROBLEM (NORMAL FUEL FLOW; OIL TEMP; OIL PRESSURE; RPM; MANIFOLD PRESSURE -- WHICH WAS 25 INCHES AT THE TIME). A REDUCTION IN PWR STOPPED THE VIBRATION. I ADVISED CTLR THAT I HAD A VIBRATION AND MUST GET DOWN IMMEDIATELY ALTHOUGH I CURRENTLY HAD PARTIAL PWR. I ENRICHED MIXTURE; INCREASED RPM; AND FLEW VECTOR TO QUAKERTOWN ARPT WHICH HE GAVE AS 8 MI AWAY. HE ASKED IF THIS WAS EMER AND I SAID YES. I HAD BECOME CONCERNED THAT NOT KNOWING THE CAUSE OF THE PROBLEM COULD RESULT IN A WORSE PROBLEM BEFORE REACHING THE ARPT. I CONCENTRATED ON FLYING THE VECTOR AND MONITORING THE INSTS. WHEN NOTIFIED THAT I WAS STILL SEVERAL (POSSIBLY 5 OR LESS) MI FROM THE ARPT; I NOTICED THAT I WAS FLYING OVER AN ARPT WITH FIXED DISTANCE MARKINGS WHICH WAS PROBABLY NOT QUAKERTOWN. I ASKED THE CTLR ABOUT IT. HE RESPONDED PENNRIDGE. I SAID I WANTED TO LAND THERE. HE SAID OK AND CALLED PENNRIDGE ON TELEPHONE. I MADE SUCCESSFUL LNDG -- END OF EMER. A MECH WAS AVAILABLE AND WORKED ON MY PROBLEM. IT WAS DETERMINED THAT 1 FUEL INJECTOR HAD CLOGGED CAUSING THE VIBRATION. THIS MECH AND OTHERS HAVE SAID TO ME THERE WAS NOTHING I COULD HAVE DONE TO PREVENT IT; AND THE VIBRATING WOULD HAVE BECOME WORSE OVER TIME DUE TO OVER-RICHNESS ON OTHER 5 CYLINDERS. ALLENTOWN FSDO REQUESTED AN M AND D RPT FROM THE MECH WHICH HE WILL SUPPLY. IN RETROSPECT; IT MIGHT HAVE BEEN PREMATURE TO GO ALL THE WAY AND SAY 'EMER'; BUT FEAR OF THE UNKNOWN WAS PROBABLY MY MAIN INFLUENCE EVEN THOUGH A SUCCESSFUL OUTCOME WAS VERY PROBABLE. IN THE FUTURE DURING SUCH OCCURRENCES I WILL TRY MY BEST TO REMAIN CALM AND IN CTL (NOT GO ALONG FOR THE RIDE) AND WORK WITH ATC IN A PROFESSIONAL WAY. I AM SURE I WOULD SAY 'EMER' AGAIN IF I THOUGHT IT NECESSARY. I FOUND THE CTLRS EAGER TO HELP AND VERY COOPERATIVE BUT I WONDER WHY THEY WOULD HAVE VECTORED ME FURTHER AWAY TO AN ARPT WITH A SHORTER RWY.