Potential Buy 1997 GSX

[asshanson]

Open loop disregards the oxygen sensor and goes off the table values (for high throttle, first bit after starting the car, etc).
Closed loop is using o2 feedback to make the AFR more rich or more lean. If it's consistently lean or rich, this will turn into a long term fuel trim adjustment.

If it's only running like crap in closed loop, take a look at the long and short term fuel trim and o2 volts, maybe your sensor is going out. Did you say you have a wideband simulating a narrowband?