Hi, I have had my Aveo for 4 years now. Never had any issues, until a couple months ago. The idle started running rough and I had issues accelerating, which was made worse with the AC running. The engine light came on and was P0301 for a misfire, I replaced the spark plugs which helped a little. But the light was still on and still has the same issues. I than ordered a replacement ignition coil pack with all new spark plugs as well, I replaced them all last night and while the light was on the car drove brand new with the air conditioning running. When I drove it this morning before I was going to take it to autozone to get the code read, the light went off, than later on I went to drive and the light was back on and the car had issues accelerating while the air was on, so I turn the air off and no issues, however, I took it in to get the code read and now I have a P0301 and P0420. Can anyone point me in the direction which isn't going to cost me thousands of dollars or selling my car?