GS INDICATOR GIVES ERRONEOUS INFO. FLC EXECUTES GAR.

Narrative

WHILE ON THE ILS APCH TO RWY 13R; I EXECUTED A GAR DUE TO; WHAT I PERCEIVED AS; UNRELIABLE NAV INFO. AS WE WERE APCHING THE FAF AND BEGINNING TO CAPTURE THE GS; THE GS INDICATIONS BECAME VERY ERRATIC. INDICATIONS WERE NORMAL WHEN SUDDENLY THE GS DEFLECTED FULL SCALE UP AND ALMOST IMMEDIATELY FULL SCALE DOWN. I STOPPED MY DSCNT UPON THE FIRST GS DEV; AT ABOUT 2600 FT STILL IMC; THEN EXECUTED A GAR ONCE THE GS DEFLECTED AGAIN. WE INFORMED TWR OF THE GAR AND RECEIVED A RATHER CONFUSING INSTRUCTION TO 'CLB TO 2000 FT ON RWY HDG; THEN AT DEP END CLB TO 3000 FT.' THESE INSTRUCTIONS WERE IMPOSSIBLE TO COMPLY WITH AT THE TIME; SINCE WE WERE CLBING; GAR PROCS; AND STILL IMC; UNABLE TO IDENT DEP END. I INITIALLY ATTEMPTED TO COMPLY WITH A DSCNT TO 2000 FT FROM ABOUT 3000 FT; AFTER THE GAR; BUT THIS WAS A VERY UNCOMFORTABLE AND DIFFICULT MANEUVER. ONCE THE DSCNT WAS STARTED WE RECEIVED A 'TFC; TFC' ALERT FROM OUR TCASII; AND AT THE SAME TIME RECEIVED A NEW CLRNC TO 'CLB TO 3000 FT IMMEDIATELY.' WHEN STABLE AT 3000 FT AND ON A VECTOR BACK TO DAL; WE ASKED IF THE ILS TO RWY 13R WAS OPERATING NORMALLY AND THE RESPONSE WAS 'YES.' 2 FACTORS STARTED OUT FOR ME AFFECTING THIS SIT. FIRST THE GS INDICATIONS WERE VERY UNUSUAL AND I HAVE SEEN THIS HAPPEN BEFORE WITH THE USE OF CELL PHONES ON BOARD THE ACFT. ON DOWNWIND FOR OUR NEXT APCH INTO DAL; I ASKED THE PAX TO TURN OFF AND NOT USE THEIR CELL PHONES. SECONDLY; THE CONFLICTING ALT INSTRUCTIONS DURING OUR GAR WERE VERY CONFUSING. MY FO WAS READING THE MISSED APCH PROCS; WHICH INCLUDE A CLB TO 5000 FT; AND RECEIVING THE 'CLB TO 2000 FT;' LATER CHANGED TO 'MAINTAIN 3000 FT.' OF COURSE; TFC CONCERNS PLAYED A MAJOR ROLE IN THE INSTRUCTIONS WE RECEIVED. WITH OUR UNEXPECTED GAR; AS VISUAL APCHS WERE BEING FLOWN; SOME QUICK DECISIONS HAD TO BE MADE. EVERYONE INVOLVED WAS TESTED DURING THIS SHORT TIME FRAME; AND CORRECT ACTIONS WERE TAKEN. OUR SECOND APCH INTO DAL WAS UNEVENTFUL AND ALL ILS INDICATIONS WERE NORMAL DURING OUR VISUAL APCH.