I just purchased a 90 civic DX from a gentlemen the other day with 193k on the clock. Car was taken car of pretty decently mechanically but I noticed some issues driving the other day home from work. at part throttle (~25%) the car is fine, but trying to accelerate harder in the lower RPM range the car hesitates and seems to buck or miss a little. No pops or strange noise, just hesitation. I also noticed that sometimes the idle goes up and down when it sits idling for extended periods of time, (after 20 or so seconds). The car has no tach, but i would say the dip is between 1200 and 400rpm that it will bounce between, up and down. I am guessing this is the IACV needing to be clean. But the accel is what i am not sure about. The car had a CEL come on whilst on the highway, and the ECU was giving code 1 for the o2 sensor. I ordered an o2 sensor even though the light was off today, I also ordered an air and fuel filter and plugs as well to start cheap. The car has a new distributor that was installed literally right before I bought it. I am thinking maybe he messed up the ignition timing somehow so I was going to check that as well. The car starts fine and revs up well. Just the idle and while under load that I get these issues. No smoke out of the exhaust or funny smells. Just wondering what would be to look at next. Thank you!