A B737-300 CREW; ASSIGNED RWY 24R AT LAX; TUNED IN THE RWY 25L ILS AND PROCEEDED INBOUND UNTIL QUERIED BY THE TWR CTLR.

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EARLIER IN THE DAY WE HAD EXPERIENCED SOME PROBS WITH THE RNAV DEP AND AUTOPLT FUNCTION. WE STARTED THE CIVIT ARR TO RWY 25L. THE FO APPROPRIATELY DIALED IN THE LOC FREQ FOR THAT RWY. WE WERE RECLRED FOR THE MITTS ARR TO RWY 24R. THE FO REPROGRAMMED THE CDU FOR THIS ARR; BUT DID NOT CHANGE HIS LOC FREQ TO THE NEW RWY. THE LNAV TRACKED PROPERLY ONTO THE ARR. WHEN I DISENGAGED LNAV; I PUT IN THE SAME FREQ (THE WRONG ONE) THAT THE FO HAD IN HIS RADIO PANEL EVEN THOUGH I HAD THE PROPER APCH CHART OUT. WE BOTH SAW THE LOC SHOWING THE COURSE OFF TO THE L. THE FO EVEN MENTIONED THAT THE LNAV WAS SCREWING UP AGAIN. I BEGAN A SHALLOW TURN TO THE L TO JOIN THE LOC COURSE. SHORTLY AFTER THAT THE CTLR CALLED AND SAID IT LOOKED LIKE WE WERE TAKING RWY 25L AND GAVE US A R TURN TO REJOIN RWY 24R LOC. AT THIS TIME WE REALIZED OUR ERROR. A REJOIN WAS QUICKLY ACCOMPLISHED. THERE WAS NO TFC CONFLICT THAT I AM AWARE OF. EARLIER; AUTOPLT AND LNAV PROBS CAUSED US TO BELIEVE THAT THE ACFT HAD NOT BEEN FULLY CTRED ON COURSE WHEN WE DESELECTED LNAV. THE CHANGE OF ARRS CAUSED THE CONFUSION WITH TUNING THE WRONG ILS FREQ.