EMERGENCY DECLARED DUE TO ENGINE PROBLEMS.

Narrative

AT LEVEL FLT; I REDUCED RPM AND BEGAN TO LOSE MP PRESSURE WHICH CAUSED IMMEDIATE LOSS OF ALT AND AIRSPD. I WENT THROUGH EMER CHKLIST AND SQUAWKED 7700 AFTER LOSING ALT AND UNABLE TO ARREST DSCNT I DECLARED AN EMER. AFTER COMPLETING CHKLIST I INCREASED RPM TO ORIGINAL SETTING OF 2500 RPM AND MP; ETC STABILIZED. CENTER WAS VERY HELPFUL AND I THEN CANCELLED THE EMER. UPON LNDG A LOOSE CLAMP AND HOSE WAS DISCOVERED AND REPAIRED ON THE TURBOCHARGER. THE AIRPLANE WAS THEN TEST FLOWN AND THE PROB WAS CORRECTED. THIS HAD BEEN UNDETECTABLE DURING RUNUP AND DURING CLB. ONE OF MY CONCERNS (OUTSIDE OF THE OBVIOUS PROB) WAS THAT I LOST 500' BEFORE I WAS ABLE TO NOTIFY THE CENTER. I BELIEVE I SQUAWKED 7700 AFTER AROUND A 300-400' LOSS IN ALT. I WAS CONCERNED ABOUT AN ALT DEVIATION VIOLATION; BUT ACTED AS QUICKLY AS POSSIBLE TO NOTIFY THEM W/O SACRIFICING MY CONTROL OF THE ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES HAD SOME PROB ON TRIP STL TO DCA. MECHS WORKED ON ACFT AND THOUGHT PROB WAS WASTE GATE STICKING. LUBRICATED AND SEEMED OK. ON RETURN TRIP WHEN LEVELING AT CRUISE DIFFICULTIES OCCURRED. RPTR FELT DECLARING EMER WAS BEST WHEN UNABLE TO HOLD ALT ASSIGNED. WANTED TO BE SURE ATC KNEW WHERE HE WAS. HE FEELS HE RECEIVED SUPERB COOPERATION. THE LOOSE CLAMP WAS ALLOWING TURBOCHARGER TO DEVELOP ONLY 1/2 OF PWR IT SHOULD.