B737 CAPT BECAME DISTR BY POSSIBLE ENG INDICATION PROB AND OVERSHOT RWY HOLD SHORT LINE; BUT DID NOT ENTER THE RWY.

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PASSED HOLD SHORT LINE OF ACTIVE RWY. I CONTACTED TWR FOR TAXI CLRNC SINCE TWR WAS WORKING BOTH GND AND TWR. WE WERE INSTRUCTED TO TAXI TO RWY 9L AND 'HOLD SHORT OF RWY 13 AT TXWY A.' WE ACKNOWLEDGED THE CLRNC AND I MADE A NOTE OF THE INSTRUCTIONS. AS WE BEGAN THE TAXI; WE HAD SOME LARGE FLUCTUATIONS OF THE #2 ENG VIBRATION GAUGE. THE QRH WAS REFERRED TO AND AS I WAS REVIEWING THE QRH WITH THE CAPT; WE TAXIED PAST THE RWY 13 HOLD SHORT LINE AT TXWY A. AT THIS TIME; BEFORE OUR ACFT ENTERED THE RWY SURFACE; THE CTLR NOTICED OUR POS AND ADVISED US TO IMMEDIATELY CROSS THE RWY. WE THEN LOOKED TO THE R AND SAW A DASH 8 (I BELIEVE) ON FINAL APCH. THE CAPT DECIDED THE SAFER COURSE OF ACTION WAS TO REMAIN STOPPED SHORT OF THE RWY SURFACE AND I CONCURRED. I ADVISED TWR WE WOULD HOLD SHORT OF THE RWY SURFACE. THE CTLR ISSUED A GAR TO THE ACFT ON FINAL. WE WERE THEN INSTRUCTED TO CONTINUE TAXI TO RWY 9L. CONTRIBUTING FACTORS WERE ATC WORKING BOTH TWR AND GND; A SUNNY DAY VFR WHICH MAY HAVE LED TO SOME COMPLACENCY; NOT BEING ADVISED THERE WAS LNDG TFC ON RWY 13 AS PART OF THE CLRNC; AND FOCUSING TOO MUCH ATTN ON THE DISTR OF THE ENG VIBRATION GAUGE. EVEN THOUGH I HAD THE RWY DIAGRAM OUT AND WROTE DOWN THE CLRNC; I REMOVED MYSELF FROM THE NORMAL DISCIPLINE OF CHKING TXWYS AND RWYS BEFORE XING. I FELL INTO THE TRAP OF LOSING SITUATIONAL AWARENESS WHILE WORKING WITH THE QRH AND NOT REALIZING HOW CLOSE WE WERE FROM THE START OF TAXI TO THE HOLD SHORT LINE OF RWY 13. (IT ALL HAPPENED QUICKLY.) IN HINDSIGHT; A PROC OF STOPPING THE ACFT FOR ANY CHKLIST; INCLUDING THE QRH; WOULD HAVE BEEN A BENEFICIAL PROC TO FOLLOW.