DC9-30 FLT CREW INCUR AUTOPLT PROBS AND OVERSHOT DELZY INTXN XING RESTR ON THE MSP KASPR STAR. AUTOPLT OVERRIDES PLT; CHANGING FROM 3000 FPM TO 6000 FPM.

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DAY VFR/VMC. KASPR 2 ARR INTO MSP. ATC SAID TO DSND (PLT'S DISCRETION) TO FL240; CROSS DELZY INTXN AT 11000 FT. DSCNT WAS PLANNED USING COCKPIT DSCNT WHEEL; ADJUSTED FOR WIND AND NO SPD REDUCTION REQUIRED. AUTOPLT HAD GIVEN US SOME PROB ON PREVIOUS LEG. THE DSCNT OR VERT SPD WHEEL WAS NOT GIVING THE AUTOPLT THE REQUESTED AMOUNT OF CLB OR DSCNT. ALSO; THE AUTOPLT JERKED THE YOKE OFTEN. WHEN USING AUTOPLT EARLIER; IT MISSED ALT LEVELOFF BY +/-100 FT TO +/-200 FT. ON THE DSCNT; USING NORMAL PROCS; THE AUTOPLT WAS SET TO 3000 FPM DSCNT; YET ONLY DID APPROX 1000 FT. I INCREASED THE RATE; BUT WAS ALREADY BEHIND MY DSCNT PROFILE. I ADDED SPD BRAKES AND WAS ABLE TO INCREASE RATE TO 4000-5000 FPM. THE AUTOPLT PITCHED OVER AND THE RATE WAS 6000+ FPM RATE OF DSCNT. AUTOPLT WAS TURNED OFF AND I MANUALLY FLEW THE ACFT. WE/I OVERCOMPENSATED AND WE WERE HIGH ON OUR DSCNT PATH. WE CROSSED THE REQUIRED ('DELZY') INTXN AT 11000 FT; BUT OVERSHOT TO 10400 FT ON CAPT'S SIDE; 10200 FT ON FO'S SIDE. WE CALLED ATC AND NOTIFIED THEM WHILE CLBING BACK UP TO 11000 FT. AUTOPLT WAS TURNED BACK ON. I CONTACTED MSP TRACON UPON LNDG AND TALKED TO SUPVR. I ALSO WROTE UP THE AUTOPLT AND BRIEFED MAINT.