1992 Nissan Sentra reverse problems

My car runs great for being 18 yrs old. Last week after driiving home from work I put car in revers and it would jump when you gave it gas and sometimes stall. This is only happening in reverse. I was clueless, so I started looking at things under the hood and I pulled out the clutch/inhibitor relay the car would not start with it out. I put it back in and the car started and when I put into reverse it was fine. I drove the car for a week, no problems untill today. I tried the same thing again but to no avail. What else could it be?