2011 Aveo Codes P0301 and P0420

[mattw1013]

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?

[JB_Fraser]

I would make sure I had a 'visual' that you have good spark (I know you changed the plug and coil pack)you can pull the plug or get a tester to verify.
If that was fine then a compression tester (about $30) and you can compare with other cylinders and you shouldn't see differences of more than 10-15%.
Replace or swap the fuel injector, if you swap it and your code changes to another cylinder , then you'll know its bad.
I think your P0420 code is due to your engine exhausting excessive un-burnt gases because of the misfire on cyl1.

That would be my route of attack, I wouldn't bother with the AC component of the problem until I knew the engine was running efficiently and smooth, after all, I can feel the difference in my 2005 running 4 good cylinders, and your running your ac off only 3 !

[Alan B]

I am on it!