SF340 PIC RPT ON IMPROPER MAINT PRACTICE OF AN MEL ATTEMPT ON HIS ACFT'S ILS RECEIVER AFTER A PORPOISING MANEUVER BY HIS ACFT ON ILS FINAL APCH WHEN ARPT WX MINIMUMS WERE IFR.

Narrative

ON APCH INTO RWY 35R; SHORTLY AFTER XING THE LOC OM; BELOW 1800 FT AGL; CAPT FLYING; AUTOPLT COUPLED ILS APCH. LNAV SELECTED; THE ACFT PITCHED NOSE DOWN BTWN 5-8 DEGS; FOLLOWING THE PINK COMMAND BARS AND THE GS FLY-DOWN INDICATION. THIS WAS FOLLOWED BY A SERIES OF PITCH OSCILLATIONS. THE RED FLT DIRECTOR AND INTERMITTENT RED GS FLAGS ILLUMINATED. THE AUTOPLT REMAINED ENGAGED. I DISCONNECTED THE AUTOPLT AND OBSERVED THE FO'S FLT INSTS SHOWING NORMAL WITH A SLIGHTLY BELOW GS INDICATION AND A FLT DIRECTOR RED FLAG. I XFERRED CTL TO THE FO AND HE LANDED THE ACFT SUCCESSFULLY. AFTER TAXI IN; WE CONTACTED MOC. MAINT CAME TO THE ACFT. EVENTUALLY THE AVIONICS PERSON CAME TO THE ACFT. HE PUSHED THE GLARESHIELD GS TEST BUTTON AND SAID IT'S OK. I INSISTED THAT I WOULD NOT ACCEPT A GS MEL IN IMC AND THE AVIONICS TECHNICIAN SAT DOWN AND TUNED AND OBSERVED THE GS. AFTER A FEW MINS; THE L GS FAILED. AFTER A FEW MORE MINS; IT CAME BACK. THE AVIONICS TECHNICIAN AND MGR STATED THAT THEY WERE GOING TO MEL THE GS. I INSISTED THAT I WOULD NOT TAKE THE AIRPLANE AND ADVISED THEM I WOULD BE FILING AN ASAP RPT. AFTER THIS STATEMENT; I WAS REQUESTED TO LEAVE THE COCKPIT. THE MGR WHO SPOKE VIA CELL PHONE WITH MOC MAINT MGR THEN BROUGHT OUT A TEST BOX THAT SEEMED TO INDICATE THE L-HAND GS WAS WEAK. THEY PROCEEDED TO REPLACE THE L-HAND NAV RADIO.