DC9 CREW HAD ALT OVERSHOT IN N90 CLASS E AIRSPACE.

Narrative

CLBING OUT FROM JFK CLRED TO 17000 FT BEING VECTORED TO NEION (LGA 322 DEG RADIAL; 42 DME). I CALLED 2000 FT TO GO; THEN 1000 FT TO GO. THE AUTOPLT STARTED MAKING JERKY MOVEMENTS WITH THE ELEVATOR. I LOOKED DOWN TO CHK THE TAB INDICATORS. AT ABOUT THAT TIME THE ALT ALERTER WENT OFF. I LOOKED UP AND THE ALTIMETER SAID 17700 FT. I DIRECTED THE FO TO GET BACK TO 17000 FT AND I CHKED THE TCASII. THERE WERE NO ACFT PAINTING ON THE TCASII. THE CTLR SAID HE NEEDED US AT 17000 FT AND ASKED US WHAT OUR ALT WAS. AT THAT TIME WE WERE PASSING BACK THROUGH 17300 FT. SO I SAID WE WERE AT 17300 FT AND CORRECTING; THEN APOLOGIZED TO THE CTLR. NOTHING ELSE WAS SAID ABOUT THE INCIDENT. SUPPLEMENTAL INFO FROM ACN 482252: DEPARTED JFK TO DTW. WE WERE CLRED UP TO 17000 FT AND AT APPROX 15000 FT I ENGAGED THE AUTOPLT. SHORTLY AFTER ENGAGEMENT; THE AUTOPLT BECAME ERRATIC AND BOTH THE CAPT AND I MADE THE GESTURE TO DISENGAGE IT. I CONTINUED TO HAND FLY AND REGAIN CTL TO STABILIZE THE ACFT. ATC THEN ISSUED A VECTOR TO INTERCEPT A RADIAL OUTBOUND WHICH THE CAPT WAS READING BACK AND JOTTING DOWN. AS I ATTEMPTED TO TUNE IN THE VOR AND SET THE RADIAL; I ACCIDENTALLY OVERSHOT THE ALT OF 17000 FT BY APPROX 500 FT. I IMMEDIATELY MADE THE ATTEMPT AND RETURNED TO 17000 FT. ATC ADVISED THAT OUR CLRED ALT WAS 17000 FT AND WE ACKNOWLEDGED.