Hey, I'm new here and new to the auto scene as well. I'm learning a lot however for starters. So my current issue is a rough idle with my 1990 Accord. In park it gets around 600-700 RPM's and once you put it in gear, it starts shaking something fierce. Once actually driving the vehicle at higher RPM's it actually smooths out. Another thing would be that once the AC is turned on, it shakes even harder. I have noticed that once put into gear, the RPM's drop below 600 but I don't think it does this consistently (will check and give more info once done.). Some other info to help out, the previous owner did have a bad alt belt on there (I replaced it with a new one), the battery is at 12.5v but after a quick test, I was told it's a bad battery. I've also changed out the spark plugs and wires and am currently running the NGK's on there as should. Last but not least, the ecm is dishing out a code for the oxygen sensor (code #1). If any other info is needed let me know and thanks in advance for any assistance.

Update: Idle drops and returns to normal when put in gear and when A/C is turned on.