Nikon FG-20 Meter problem

I just picked up a FG-20 in really nice cosmetic condition and what I though was perfect working condition. The problem I see now is that the meter is erratic in aperture priority. Sometimes it will give me the correct exposure and most of the time it's 1/90th or so and the meter needle will jump around. The batteries are fine and the meter works great in manual and doesn't jump around. All of the shutter speeds are fine in manual also.

Any ideas?

It may simply down to old age! (Like a lot of us). Joking apart, the electronic shutters and the meters do need servicing every now and again especially as these cameras will be close on 25 yrs old. If there is anything seriously wrong (I doubt it) then the spares situation for these oldies but goodies will be very limited. If as you say it is in good cosmetic condition then the chances are it has had very little use and a service may bring it back to full life.

You could try a new set of batteries, but before you fit them, thoroughly clean out the battery compartment of any grime especially on the internal contact. The batteries themselves should be clean and grease free and the cap for the battery compartment should be similarly cleaned and grease free.

must be a short somewhere.