1988 Mazda RX7 Loss of Power - Jerking

Engine Performance problem
1988 Mazda RX7 Two Wheel Drive Manual 118000 miles

My RX7 runs very strong, however every once in a while it will lose power, and begin jerking violently. Similar to when you let out the clutch & don't accelerate, but the engine wont die, it'll continue to jerk until I depress the clutch & keep it pressed down. The only way I can get it back to the house is by placing in 2nd gear & slowly let off the clutch, while accelerating. This process will only allow me to go about 10 miles per hour though. Odd thing is, this only happens every other day. The car drives fine when not being possessed. Any ideas on what I should check?