In the meantime, you could just disconnect the O2 sensor and the car will run on open-loop if the problem is really that bad. Like said above, if it gets worse when warm, that is a strong indication of possible O2 sensor failure. If you can, get someone with a DSO to see if it is working properly, a DMM with a High/Low setting may work as well. Good Luck! Let us know what the problem was when fixed.
- Aaron