ACFT EQUIP PROB CREATES NEED FOR FLT ASSIST.

Narrative

I DEPARTED CAD IN GOOD VFR WX. I WAS FLYING TO THE MOP VOR AND THEN S TO LAN. UPON PASSING TO THE W OF MOP I COULD SEE SNOW SHOWERS IN THE DISTANCE. I HAD RECEIVED A WX BRIEF SO I KNEW THEY EXISTED AND THOUGHT I MAY ARRIVE AT THE SAME TIME. APPROX 10 MI S OF ALMA; MI; I BEGAN TO EXPERIENCE SERIOUS ENG ROUGHNESS. ENOUGH FOR ME TO SEEK RADAR VECTORS TO THE NEAREST ARPT FROM LAN APCH. THEY GAVE ME VECTORS FOR ALMA WHILE I WAS IN MVFR AND WAS ADJUSTING MIXTURE; THROTTLE; AND CARB HEAT IN AN ATTEMPT TO KEEP THE ENG RUNNING. I MANAGED TO REACH 2300 RPM IN THE CE-150 AND ADVISED LAN APCH THAT I COULD MAKE LAN. SO; THEY GAVE ME VECTORS FOR THE LAN ILS RWY 10R FINAL APCH COURSE. AT APPROX 15 MI N OF THE IONIA ARPT; I EXPERIENCED ENG ROUGHNESS AGAIN; SOMEWHAT MORE VIOLENT. I WAS NOW IN IMC WITH SNOW. I ONCE AGAIN ASKED FOR VECTORS TO THE NEAREST ARPT. THEY GAVE ME VECTORS FOR IONIA AND I BEGAN TO HEAD FOR IT. I MANAGED TO ADJUST THE ENG CTLS ENOUGH TO HOLD ALT AND 2000 RPM. I CALLED LAN APCH AGAIN AND TOLD THEM I FELT I COULD MAKE LAN. THEY GAVE ME VECTORS FOR THE LAN ILS RWY 10R APCH; AND I INFORMED THEM THAT WE PROBABLY ONLY HAD 1 CHANCE TO MAKE THE APCH AND I ONLY WOULD BE CAPABLE OF SHOOTING THE LOC APCH. I TOLD THEM THAT I WOULD LIKE TO KEEP THE APCH IN TIGHT AND THAT I WOULD LIKE A RADAR/SURVEILLANCE APCH. THEY SAID THAT WOULD BE NO PROB. THE LAN APCH/TWR STAFF WAS; AS USUAL; GREAT AND COOPERATIVE. I FLEW THE SURVEILLANCE APCH AND SPOTTED THE APCH LIGHTS AND WAS CLRED TO LAND ON 10R AT LAN. I LANDED WITH THE ENG SEEMING TO RUN WELL AT NORMAL PWR AND IDLE. THE TWR NEVER ASKED ME TO CONTACT THEM; BUT I KNOW THE TWR STAFF AND I WENT AND SPOKE WITH THEM. THEY SAID THAT I DID A NICE JOB AND THAT NOTHING WENT WRONG AS FAR AS THE TEXTBOOK IS CONCERNED. I FEEL THAT I HAD A SERIOUS ENCOUNTER WITH CARB ICE; OR MY MAGNETOS OR PLUGS WERE SERIOUSLY MALFUNCTIONING/NOT PERFORMING UP TO STANDARDS. I AM HAVING NEW MAGS PUT ON AND THE SPARK PLUGS AND WIRES INSPECTED. THE EXHAUST AND CARB ARE ALSO BEING COMPLETELY INSPECTED.