AN SF340 FLT CREW FLEW THROUGH THEIR ASSIGNED ALT IN DESCENT WHEN THEY FAILED TO RESET THEIR ALTIMETERS; IN PART BECAUSE THEY WERE DISTRACTED BY A MINOR ENG PROBLEM.

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WE WERE INBOUND TO ZZZ CRUISING AT FL190. WE HAD A L INTAKE LIGHT THAT CAME ON SEVERAL TIMES; FOLLOWED BY A ROLLBACK ON THE L ENG. I WAS THE PF BUT XFERRED CTL TO THE FO SO I COULD COMMUNICATE WITH MAINT ON COM #2. DURING THIS TIME; CTR TOLD US TO DSND TO 9000 FT. I WAS TALKING WITH MAINT AND FORGOT TO SET MY ALTIMETER TO A LCL SETTING DSNDING BELOW FL180. MY FO FORGOT AS WELL. AFTER TALKING WITH MAINT; I RESUMED MY ROLE AS PF. THE FO BEGAN THE DSCNT CHKLIST. CTR SWITCHED US TO APCH WHILE THE FO WAS STILL GETTING THE ATIS. I CHKED ON WITH APCH JUST AS WE WERE LEVELING AT 9000 FT. WHEN CHKING ON; I TOLD APCH WE WERE LEVELING AT 9000 FT BUT DIDN'T YET HAVE THE CURRENT ATIS. SHE REPLIED WITH A CURRENT ALTIMETER OF 29.61. AS I PUT IN THE NEW ALTIMETER; I REALIZED WE HAD NEVER RESET THE ALTIMETERS FROM 29.92 AND WITH THE CURRENT LCL SETTING WE WERE APPROX 300 FT BELOW OUR ASSIGNED ALT. ATC DID NOT SAY ANYTHING ABOUT NOTICING THE DEV AND I CORRECTED TO 9000 FT WITH THE CURRENT SETTING. I WAS DISTR TALKING WITH MAINT DURING DSCNT AND FORGOT TO RESET THE ALTIMETER. BECAUSE THE FO WAS ASSIGNED PF DUTIES HE DID NOT BEGIN THE DSCNT CHK AS EARLY AS NORMAL; DELAYING GETTING A CURRENT SETTING THAT MIGHT HAVE HELPED US CATCH OUR ERROR. IN ADDITION; ATC NEVER GAVE US A LCL ALTIMETER SETTING WHEN THEY ISSUED THE DSCNT CLRNC.