My 91 has started to intermittantly backfire at wide open throttle and have a loss of power throughout the rpm band. I pulled the codes and all I get is 11 - all systems normal.
The most simple solution could be a dirty MAF. I had the same symptoms, carefully cleaned the little wire sensors with a Q tip and alcohol (which were black). It took care of the backfiring and loss of power, the difference was drastic, it felt like I gained 70 rwhp back.