FS2002 Autopilot not holding altitude any suggestions

Hi all, I know some of you may have come across this in the past when using FS2002 and probably will remember how it was solved... I am still using Fs2002 and the autopilot doesn't seem to hold the altitude. I have just reinstalled 2002 and remember that I used to have the same problem until I read somewhere in one of these post about editing the scenery.cfg file in the fs2002/directory. Can anyone remember how it was done? Other suggestions are welcome, the sim used to work brilliant before I re-installed fs2002, I was just bored and thought I'd clear out the junk thats making my system a mess.ThanksRay