p0305 code cylinder #5 misfire

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2002 mazda mpv 3.0 i have a p0305 code i interchanged the coil and still got the code. but what i noticed i disconected each coil one at a time at idle rpm (700) and every time i disconected one the engine would shake exccept when i got to # 5 nothing would happen when i incremented idle speed i disconnected 5 again then i noticed change in engine. I think its a clogged injector please advise.