NMAC. POSSIBLE OP ERROR.

Narrative

WX AT SNA WAS SKY OBSCURED 1000 FT OVCST; VISIBILITY 2 MI; RAIN; FOG WITH THE TOPS AT 8000 FT. WE WERE VECTORED ACROSS THE LOC FOR A R DOWNWIND AT 170 KTS. ON BASE LEG WE WERE ASKED TO SLOW TO 150 KTS; WE COMPLIED. ON THE INTERCEPT HDG WE WERE CLRED FOR THE ILS RWY 19R AND INSTRUCTED TO SLOW TO APCH SPD. WE CROSSED LEMON INTXN AT 135 KTS (APCH SPD) AND CONTACTED THE TWR. TWR ISSUED A GAR FOR SLOW GA ACFT ON THE APCH AHEAD OF US. NOW ON THE SECOND APCH; INTERCEPT HDG TO THE LOC; WE WERE ISSUED A CLRNC TO DSND TO 3000 FT; MAINTAIN 3000 FT TILL ESTABLISHED; CLRED FOR THE ILS APCH RWY 19R. ESTABLISHED INBOUND; IMC; OUTSIDE OF SNAKE INTXN AT 3000 FT A TA POPPED UP ON THE TCASII 500 FT BELOW. I ASKED APCH CTL IF HE HAD THE TFC. DURING MY XMISSION THE TARGET SHOWED 400 FT THEN 300 FT BELOW AND CLBING. THE CTLR SAID; 'YOUR CLRED TO 4000 FT.' I INSTRUCTED THE FO TO EXECUTE A MISSED APCH; SIMULTANEOUSLY WE RECEIVED AN RA TO 'CLB CLB CLB NOW.' IN THE TIME THE GAR WAS ACCOMPLISHED THE TARGET; ON THE TCASII; WAS SHOWN AT OUR ALT AND PASSED THROUGH OUR AIRPLANE SYMBOL. TCASII ISSUED A 'CLR OF CONFLICT' COMMAND SHORTLY AFTER. WE WERE ISSUED A R DOWNWIND VECTOR FOR ANOTHER APCH; WHICH WAS ROUTINE. WE WERE IMC THE ENTIRE TIME BELOW 8000 FT AND DID NOT HAVE GND CONTACT UNTIL 500 FT AGL.