Fly from Portland wrote on Jun 15^th, 2014 at 5:40am:

Hi Lou I have been practicing landings for a few weeks and I'm trying to keep from porpoiseing in the glide slope. Is there any good technique to stop this from happening. Auto GS is the worst for this condition at KJFK. I am pretty sure I am low enough to be under the GS when I capture it. The manual GS usually keeps me at -700 fpm on descent which is what I want. I am starting at 1500 alt and about 8 or 9 miles out from rwy 22R. Any suggestions would be helpful. :-/

I had porpoising with the 727 A/P pilot as well. Are you using SP2 or are you running Acceleration? When I reinstalled FSX I changed from SP2 to Acceleration and the porpoising problems completely stopped and the AP has been very smooth since. But, as Lou pointed out, incorrect throttle usage can also cause this problem. If you're running SP2 and not Acceleration, that could be the problem. But regardless of SP2 or Acceleration, throttles must be managed with finesse while on GS capture. Just a little insight for you.

cheers,
Brian