MD90 CREW IS TRIPPED UP BY SPEED RESTRICTION AND LATE RWY CHANGE ON THE CIVET 5 IN TO LAX.

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ON DSCNT TO LAX WE WERE GIVEN DSCNT CLRNC TO CROSS GRAMM INTXN AT FL190; THEN ASKED TO SLOW TO 250 KTS. WE WERE GOING TO BE HIGH AND FAST AT GRAMM INTXN SO ASKED APCH WHAT HE WANTED -- SPD OR ALT. WE WERE CLRED TO FL190 AND 250 KTS WITH NO GRAMM INTXN RESTR. I SELECTED INDICATED AIRSPD DSCNT ON FMC TO EXPEDITE DOWN TO FL190. WE WERE GIVEN CLRNC VIA THE CIVET ARR TO RWY 24R; A CHANGE FROM WHAT WAS BRIEFED AND PLANNED. I RESET THE FMC TO 7000 FT TO COMPLY WITH CIVET ARR; BUT NEVER SELECTED VNAV; RESULTING IN AN ALTDEV AT CAMDI OF 400-500 FT LOW. THERE WERE 4 DISTRS IN A VERY SHORT TIME THAT CONTRIBUTED TO THIS DEV: 1) CHANGE OF ARR AND RWY TO RWY 24R. 2) ACCOMPLISHING APCH CHKLIST. 3) REMAINING IN INDICATED AIRSPD WHEN MENTALLY IN VNAV. 4) FREQ CHANGE. MULTIPLE ALT CONSTRAINTS ON CIVET ARR. EXTREMELY GUSTY WINDS AND TURB ON APCH. A LEVELOFF WAS ACCOMPLISHED BACK TO 12000 FT AND THE ARR WAS RESUMED WITH NO FURTHER INCIDENT. NO COM WAS MADE TO ATC; NOR REPLY FROM ATC. NO TFC CONFLICTS WERE NOTED.