Low Power and Idle Problems with 2003 2.2L

Working on my sisters 2003 Alero with a 2.2L engine. Her service engine light had come on and she couldn't get the car to drive above 40mph. She brought it over tonight and immediately I knew the cat was plugged. It was red hot underneath and you could feel the heat from the side of the car. We don't have emmisions here so I cut out the flange between the cat and the resonator and pulled the o2 sensor and gutted the cat. We will put a new one in once we have this solved (and when she can afford it). After starting the car and letting it blow out the debris I shut down and put in the o2 sensor and use a patch piece to reconnect the exhaust. Well you can tell the exhaust is more free flowing but there is still a problem. It idles and drops dow to 4-500rpm every couple of seconds or so and is really sluggish on the take off like its not hitting all cyclinders. Once above 2000rpm it sounds smooth and I can punch it and it will hit 6-7K on the tach but I can't really tell if its getting full power as we've got snow on the ground. I have done research on this forum and to me it seems like it might be the coil pack or ignition control module. Is there a way to test these. I haven't pulled the codes yet and plan on buying a scanner tomorrow (I don't want to sit in autozones lot using theirs and will get future use out of it). I pulled the plugs and they don't look horrible but the two inner cyclinders do look a little more wet. The boots on the coil pack look like new. The other options is the O2 sensor after the cat as it was subjected to the heat. Hard to tell if a sensor went bad and kill the cat or other way around (if its the o2). Any ideas. I realize the codes would be helpful but I haven't gotten there yet. Also after pulling the batt cables for ten minutes and putting them back on the service engine light does go off. Then you start it and about 5-10 seconds later it will come on. I belive it flashes and then stays solid. I appreciate any help!

Also where does the o2 sensor that is behind the cat plug in at? Looked like the wire ran to the firewall and up?

I did resolve the problem. It was the ignition control module. Part was $103 at local dealership and is removed by 3 torx screws. I had replaced the coil pack with no real difference. When I went into the shop I talked with the mechanic and asked his opinion and he said the 2.2l eco tech engines go through the ICM's frequently and that in his opinion I was on the right track. Sure enough, got home and plugged it up and all was fine. Idle perfect and power fine and no more gas in the exhaust. The check engine light stayed off for my drive and for another day but has returned but I believe that is probably from the o2 sensor since now the cat is gutted or because when the cat was plugged it had gotten so hot that the plastic jacket on the o2 was melted back so maybe the sensor is faulty. I will pull the codes later this week but for now its running like a top.