SMA PLT EXPERIENCE PWR LOSS DURING IFR FLT AND DIVERTED TO ANOTHER ARPT UNDER INTERMITTENT PWR. FUEL LINE ICE AND ENG INTAKE BLOCKAGE IS SUSPECTED.

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I WAS ON AN IFR FLT PLAN. FLYING VMC AT 11000 FT MSL; I FLEW S AROUND AN AREA OF SNOW SHOWERS. ONCE E OF THE MOUNTAINS; I DID NOT SEE ANY CLOUDS; BUT THE AIR WAS VERY MOIST LADEN. I REQUESTED 15000 FT THINKING I COULD CLB ON TOP OF ANY THIN CLOUD LAYERS. I WAS GIVEN CLRNC; BUT WHILE CLBING I ENCOUNTERED IMC WITH MOISTURE IN THE AIR. DURING THE CLB; I FLEW INTO A CLOUD FOR WHAT SEEMED TO BE 30 SECONDS AND PICKED UP A VERY THIN ICE COAT ON 50% OF MY WINDSHIELD. I WAS BTWN LAYERS AT 13000 FT SO I REQUESTED TO REMAIN LEVEL. CLRNC GRANTED SO I STAYED AT 13000 FT MSL FOR SOME 15 MINS. THE TEMP WAS 10 DEGS BELOW ZERO. I BECAME CONCERNED OVER THE FACT THAT THIN RIME ICE WAS NOW ON MY LEADING EDGE. BECAUSE I DID NOT WANT ANY ICE TO BUILD UP; I REQUESTED 9000 FT AND WAS GRANTED 10000 FT. UPON DSNDING THROUGH 11000 FT MSL; MY ENG BEGAN TO LOSE SOME PWR. I NOTICED THE CYLINDER HEAT TEMP WAS 50 DEGS COOL. SUDDENLY; THE ENG PWR DROPPED OFF DRASTICALLY; FALTERED; GAINED PWR MOMENTARILY; AND THEN DROPPED OFF DRASTICALLY AGAIN. I INCREASED RPM'S TO 2600 RPM; AND FUEL TO RICH. BOOST PUMP ON. I DECLARED AN EMER. ANOTHER ACFT ASKED CTR IF THEY HEARD ME. CTR CONTACTED ME AND I DECLARED AN EMER STATING THAT PWR LOSS WAS OCCURRING MULTIPLE TIMES AND I WAS NOT SURE IF THE ACFT WOULD MAINTAIN INTERMITTENT PWR OR NOT. I TURNED THE ACFT TO A 180 DEG HDG AND REQUESTED LOWER CLRNC. I CANNOT REMEMBER WHAT WAS GRANTED -- MAYBE 9000 FT OR 8000 FT. I NOTICED THAT THE EGT ON ALL 4 CYLINDERS WAS PEAKING AT MAX EGT MULTIPLE TIMES. I SUSPECTED FUEL BLOCKAGE. UPON DSNDING THROUGH SOMETHING LESS THAN 9500 FT MSL; I REGAINED CONSISTENT PWR. BY THIS TIME CONVERSATIONS AS TO ALTERNATIVE ARPTS WERE DISCUSSED INCLUDING SANTA ROSA AND CHONCHAS LAKE. MY HDG WAS NOW 210 DEGS TO 240 DEGS AND MY ALT WAS BELOW WHAT I THOUGHT WAS THE MEA. I DECLARED I WAS GOING TO TUCUMCARRI (TCC). I ASKED FOR A MINIMUM ALT AND WAS GRANTED 7700. BEING THE ENG HAD REGAINED PWR; I CLBED BACK FROM WHAT I REMEMBER TO BE SOME 7300 FT OR SO MSL TO 7700 FT MSL. I PICKED TCC BECAUSE IT WAS IN LOWER TERRITORY; HAD AN APCH I COULD FLY IN PROTECTED AIRSPACE AND RAIN WHICH INDICATED WARMER AIR. I CONSIDERED; BUT DID NOT WANT TO SWITCH FUEL TANKS BECAUSE OF A FEAR OF LOSING ALL PWR. I LEFT ALL SETTINGS ALONE AS I DID NOT WANT TO TROUBLESHOOT WHILE CONTINUING IMC. I HEADED FOR THE VICTOR RTE 12. I DID NOT WANT TO ATTEMPT TO FLY BELOW THE MEA TO LOCATE THE 2 VFR ARPTS MENTIONED ABOVE. UPON LNDG AT TCC AND CLOSING FLT PLAN; I CHKED FOR WATER AND FOUND NONE IN THE L TANK. HOWEVER; IN THE OTHER UNUSED R TANK; I DID FIND WATER -- 3 DROPS. BECAUSE I NEGLECTED TO CHK FOR WATER DURING MY PREFLT BY DRAINING FUEL; I SUGGEST THAT ICE FORMED IN THE FUEL LINE CREATING A BLOCKAGE OF FUEL TO THE ENG. IT IS POSSIBLE THAT THE RAPID DSCNT FROM 13000 FT TO 10000 FT MSL CONTRIBUTED TO SUPER COOLING OF THE AIRFRAME AND ENG. IT IS POSSIBLE THAT THIN ICE MAY HAVE FORMED ON THE AIR INTAKE. CONCLUSION: ALWAYS DRAIN FUEL FOR WATER OR CONTAMINATION PRIOR TO EACH FLT. NEVER SKIP THIS TEST EVEN ONCE. DO NOT ASSUME THAT FLYING BTWN LAYERS WILL AVOID ICE BUILDUP. BE AWARE OF MEA'S -- EVEN DURING EMERS.