'09 CTS DI FE1 Luxury
AFAIK the OP has checked many of the usual suspects but not all yet. It might very well be the chains at his mileage.
The line going from the air inlet tube after the MAF sensor going back over and toward the end of the valve cover, should be plugged into the valve cover. If it is disconnected, you will have problems. It will allow air to bypass the MAF sensor and enter the motor. You probably missed reconnecting it after the valve cover gasket replacement. It probably does not explain the code you are getting now.So put valve cover gaskets on, new coils, plugs, cleaned MAF and throttle body. Did TPMS reset now I am getting a P0020 code. Anybody have any ideas? It's a camshaft bank 2 code. Bad sensor? weird it didn't pop until after I did this stuff though. I did also find that apparently last time it as at a shop there is a line that runs from between the airbox and throttle body. It plugs into intake tube and runs back over passenger side and is supposed to got into about a 45 degree boot it looks like and onto a fitting. That boot is gone. Not sure what it feeds but could that be my issue as that line isn't hooked up I found.
I think every Forum should require you to put where you live. That way if someone had a problem close to you but needed a scanner to help them with it and you had one you could help them if you knew where they lived. if they live five states away there's not much you can do without asking every time.I wish the new site had a line that showed location as the old one did; many people don't even put it in their inner profile.
Sure would help with concerns like this.