AN ACR PILOT APCHING EGLL FAILED TO REMOVE A MANUALLY SELECTED ILS FREQ AND ACQUIRED THE ILS LOC TO THE WRONG RWY.

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INITIALLY; WE SET UP FOR THE ILS RWY 27L EGLL. WHEN I SELECTED THE APCH FROM THE DATABASE AT THE TIME WE RECEIVED ERRONEOUS ILS LOCK ON SO I DECIDED TO MANUALLY SELECT THE ILS COURSE AND FREQ ON THE NAV RADIAL PAGE. WE WERE SUBSEQUENTLY GIVEN THE ILS APCH TO RWY 27R AS THEY WERE USING THE L SIDE FOR DEPS. I RESELECTED THE ILS FOR THE R SIDE AND WE WERE GIVEN AN INTERCEPT HDG TO THE LOC. SIMPLY PUT; I FORGOT TO DELETE THE MANUALLY TUNED ILS FREQ FOR THE L SIDE SO THE ACFT DID NOT INTERCEPT THE RWY 27R LOC AND WE WENT THROUGH THE FINAL APCH COURSE. PASSING THROUGH THE COURSE TWR INFORMED US THAT WE HAD GONE THROUGH THE LOC AND GAVE US A HDG BACK TO INTERCEPT. THERE WAS NO TFC CONFLICT AND WE INTERCEPTED THE RWY 27R LOC AND COMPLETED THE LNDG UNEVENTFULLY. IT WAS MY MISTAKE AND MINE ALONE AS I SHOULD HAVE DELETED THE MANUALLY INPUT LOC FREQ AND ALSO SHOULD HAVE REALIZED THAT THE WRONG LOC FREQ WAS DISPLAYED ON MY PFD. THE SHORT AMOUNT OF TIME GIVEN THE APCH CHANGE AND TRYING TO ACCOMPLISH THE BEFORE LNDG CHKLIST DISTR ME FROM PROPERLY TUNING AND IDENTING THE PROPER LOC FREQ. I ALSO REALIZE THAT MANUALLY TUNING A LOC FREQ AT AN ARPT WHERE RWY AND APCH CHANGES OCCUR OFTEN IS NOT A GOOD IDEA.