Miss under load when engine goes closed loop

Car runs fine in open loop. As soon as the engine goes closed loop, there is a noticeable stuttering miss under load. New coils and ignition module. New plugs, wires, and crank sensor. Closed loop symptoms make me believe that the PCM is driving a too-lean or too-rich condition. No OBD-I codes at all. This issue is almost identical to one listed in a thread started by a member EK2000D back in December 2013 on his aunt's 1995 Pontiac. I've troubleshot every sensor on the engine and everything looks good. I'd be curious what solved EK2000D's problem (if it did get resolved). Thanks