this situation cannot be figured out yet without a DTC code. Its like a total shot in the dark. It could be so many different things that can cause a low idle/misfires so when you find your dtc code, post it in the thread and we can figure it out most likely. When its something with a issue that is easy to reproduce, most of the time its very easy to fix. plugs, coilpack, wires, maf/map, o2 sensors, cat convert, etc etc all can effect the running of a car similar to how you have described.