There's an o-ring you need to change in the distributor shaft. I had the same problem sometime back and the guys here told me about it. It's pretty simple and it's just a couple of bucks. You can go to the Autozone website and there's a section on the left on Repair Info. Just choose your car model, year, etc and then go to the Engine Electrical section. From there, choose the Distributor section. It shows you how to open the distributor and stuff, with pictures too.
Btw, I have a 4AF too, in my '90 AE92.

Good luck!