MD83 FLT CREW DESCENDING VIA STAR; OBSERVED TFC BELOW ON TCAS; RESULTING IN 'CLIMB' RA. ENGINES WERE SLOW SPOOLING FROM IDLE AND TFC PASSED 500 FT BELOW ACFT.

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NO TA FROM EITHER CTLR. DIFFICULTY CHKING ON WITH THE FINAL CTLR DUE TO FREQ CONGESTION. SETTING SUN DIRECTLY IN FRONT OF US. EVENT OCCURRED SW OF THE LUXOR INTXN ON THE GRNPA ARR WHILE BEING HANDED OFF FROM THE INITIAL APCH CTLR TO THE FINAL CTLR. WE HAD A TCAS TA FOLLOWED BY AN RA WITH A SINGLE ENG AIRPLANE WHO APPARENTLY WAS VFR. WE HAD BEEN CLRED TO 8000 FT AND HAD JUST BEEN GIVEN THE HDOF TO THE LAS VEGAS FINAL CTLR WHEN TFC APPEARED ON THE TCAS ABOUT 3 MI AHEAD AND 1200 FT BELOW US (AT 9500 FT MSL). WE WERE AT FLT IDLE DSNDING AT 250 KTS AND ABOUT 1700 FPM. ABOUT 1 SECOND LATER WE RECEIVED A 'MONITOR VERT SPD' WARNING. THE FO WAS FLYING AND DISCONNECTED THE AUTOPLT AND IMMEDIATELY BEGAN REDUCING OUR DSCNT AND STOOD THE PWR LEVERS UP TO APPROX THE TKOF POS IN AN ATTEMPT TO LEVEL OFF 500 FT ABOVE THE TFC. THE TFC NOW WAS JUST ABOUT TO PASS UNDER US GOING THE OPPOSITE DIRECTION. THE ENGS TOOK ABOUT 7-8 SECONDS TO SPOOL WHICH IS AN UNUSUALLY LONG TIME AND THAT CAUSED AIRSPD TO BLEED OFF AS WE WERE TRYING TO LEVEL AT 500 FT ABOVE THE TFC. WE THEN RECEIVED A CLB RA JUST BEFORE THE ENGS SPOOLED AT ABOUT 230 KTS WHICH ALSO WAS SLAT EXTENSION SPD. THE CLB WAS DELAYED A COUPLE OF SECONDS UNTIL WE GOT ENG SPOOL AS WE FELT WE COULD NOT RAISE THE PITCH ANY FURTHER DUE TO AIRSPD DECAY. RECOVERY CONTINUED UNTIL WE WERE ABOUT 1000 FT ABOVE THE OTHER ACFT. THE FO RPTED TO ME HE HAD SEEN A SINGLE ENG ACFT PASS UNDER US JUST AS THE ENGS SPOOLED. I AM NOT SURE WHETHER WE CAME CLOSER THAN 500 FT OR NOT. WE WERE BOTH LOOKING INTO A SETTING SUN AND RECEIVED NO TA FROM ATC. I RPTED TO ATC THAT WE HAD RESPONDED TO AN RA AND HAD TO CLB. THIS EVENT WAS A CLOSER ENCOUNTER THAN IT SHOULD HAVE BEEN DUE TO SLOW SPOOLING ENGS. I HAVE SINCE LEARNED THIS ACFT HAS BEEN WRITTEN UP FOR THIS PROB BEFORE; AND THEN CLRED WITH NO ACTION TAKEN BECAUSE THERE ISN'T ANY REQUIRED SPOOL-UP TIME IN THE MAINT MANUAL. IF WE DID GET CLOSER THAN 500 FT; I STRONGLY BELIEVE IT WAS DUE TO THE POOR PERFORMANCE OF THE ENGS ON THIS PARTICULAR AIRPLANE. THE TCAS INFO SAYS WE WILL BE. I DO NOT SEE HOW WE CAN LITERALLY HAVE A TCAS COMMAND THAT WE CAN NOT INSTANTLY COMPLY WITH DUE TO ENG SPOOL PARAMETERS THAT ARE APPARENTLY OUTSIDE OF TCAS PARAMETERS.