A319 FLT CREW INITIATED S-TURN ON FINAL APCH TO LOSE ALT WITHOUT TWR APPROVAL.

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I WAS FLYING AS CAPT TO LGA WHERE VISUAL APCHS TO RWY 22 WERE BEING CONDUCTED. ACFT WERE BEING VECTORED TO THE E AS RWY 31 WAS BEING USED FOR DEPS. ON A NORTHEASTERLY HDG JUST PAST THE ARPT; I SLOWED TO 210 KTS. THE CTLR GAVE US A DSCNT TO 3000 FT. AS WE REACHED 3000 FT; THE CTLR GAVE US 2000 FT AND HDG 320 DEGS. CTLR ALSO POINTED OUT TFC WHICH WE RPTED IN SIGHT; AND WE WERE THEN CLRED FOR THE VISUAL APCH TO RWY 22. WE WERE APPROX ABEAM THE FAF (GREKO) IN THE DSCNT TO 2000 FT. I TURNED DIRECTLY TO GREKO AND WAS TRYING TO SLOW DOWN AS WE DSNDED. AS A RESULT; I CROSSED GREKO ABOUT 600 FT HIGH; AND IT APPEARED FOR A MOMENT THAT WE WOULD NEED TO GO AROUND. I ASKED THE FO TO ASK THE TWR IF WE COULD DO AN S-TURN ON FINAL TO LOSE ALT; BUT FREQ CONGESTION DUE TO DEPARTING TFC ON RWY 31 PREVENTED RECEIVING PERMISSION. I DID AN S-TURN TO THE L AND BACK. LINING UP ON THE RWY AGAIN; IT NOW APPEARED THAT WE COULD SAFELY COMPLETE THE APCH AND LNDG. WE WERE CONFIGURED AND STABILIZED BY 500 FT; AS OUR PROCS REQUIRE ON A VISUAL APCH. WE LANDED WITHOUT FURTHER COMMENT OR INCIDENT. I SHOULD HAVE BEEN MORE AWARE OF OUR ALT AND SPD WHEN CLRED FOR THE APCH. IN THE FUTURE; I WILL LOWER THE GEAR EARLIER TO HELP REDUCE SPD. A CONTRIBUTING FACTOR WAS THAT IT WAS A SUNNY DAY WITH MEDIUM TFC SO LGA WAS NOT ISSUING ASSIGNED AIRSPDS AS THEY USUALLY DO. ON A BUSY DAY IF YOU SLOW ON YOUR OWN; APCH USUALLY GETS UPSET. THIS RPT IS FOR THE S-TURN TO LOSE ALT ON FINAL. THE TWR DID NOT COMMENT; BUT IT WAS AN UNEXPECTED MANEUVER FOR A VISUAL APCH TO RWY 22.