USING WEAK AND SUBSEQUENTLY DETERMINED UNRELIABLE NAV RADIOS A BONANZA PLT IS DISCOVERED BY ATC TO BE BELOW GS AND OFF COURSE.

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CLRED FOR APCH APPROX 7-8 MI FROM NOLA. NEITHER LOC RESPONDING POSITIVELY. NOTICED OM FLASHING AND GS INDICATING DSCNT. ADF WAS TUNED AND IDENTED; BUT NOT POINTING. FOLLOWED GS DOWN TRYING TO SORT OUT WHAT WAS WORKING AND WHAT WAS NOT. STOPPED AT TOP OF CLOUD LAYER. APCH CTLR NOTICED MY ALT WAS LOW. CLBED BACK TO 2200 FT. APCH INDICATED I WAS ALSO R OFF COURSE. NEXT PASS WAS APPROX 1 MI FROM NOLA AND THE APCH WAS COMPLETED OK. THE AIRPLANE IS A 1978 V35B BONANZA AND IS RELATIVELY NEW TO ME. UPON ARR AT BFI; I TOOK THE PROBS TO FBO TO SORT OUT. THEY PERFORMED A NEW IFR CERTIFICATION AND DETERMINED THAT (IN ADDITION): A) ONE ILS WAS INOP; B) THE OTHER ONE WAS IN TOLERANCE BUT WEAK; C) THE ADF NEEDLE DIDN'T POINT; AND D) THE APCH COUPLER FOR THE AUTOPLT NEEDS TO BE REPLACED. I RECOGNIZE THAT I GOT SUCKED INTO A VERY BAD SIT HERE. FIRST; THE WX WAS FORECAST TO BE VFR LONG BEFORE WE LEFT LEWISTON; ID. IT STILL HADN'T QUITE LIFTED UPON OUR ARR (OBFI). WE WERE USING 'FLT FOLLOWING' AND THEY TURNED US OVER TO APCH FOR WHAT SHOULD HAVE BEEN A ROUTINE ILS APCH. I ASSUMED THE AIRPLANE RADIOS WOULD WORK AS ADVERTISED AND AS WELL AS THEY HAD IN THE RECENT PAST. I WAS QUITE SIMPLY WRONG IN THAT AND WILL IN THE FUTURE INCLUDE THE ILS IN MY ROUTINE FOR TESTING THE RADIOS. WE HAD COME FROM GEU (PHOENIX) USING THE VOR SYS IN CONJUNCTION WITH THE 2 GPS SYS ON BOARD. THAT PART SEEMED TO WORK FINE.