I just bought a month ago a 2001 3.8 Gen 4 Camaro. It was shifting a little weird. Fuel mileage has been bad and at times if felt like a miss in the engine. The car has 32,000 miles on it. So this past Friday it wouldn't start. Finally after a half hour it would start and idle at 1200 rpm, with no acceleration possible. Then once I idled it to a garage. I turned it off and it wouldn't restart. Came back the next morning, checked for codes. It had P1518, P0449, P0443. I started it and it ran very rough. While running, I tried to reset the codes and they reset and it ran perfectly. I drove it 3mile home. Shut it off in the garage and tried to restart to no avail. Same codes came up. Last night, I disconnected the battery and PCM. Check battery voltage and it was good. I also cleaned all of the grounds I could find under the hood,

So this morning, I hooked everything back up and it started fine. I jacked the car up and climbed around and found what I think may be the issue. The strap ground that runs from under the driver's side motor mount to the body was rotted into 3 pieces. I ran 2 new ground straps from the engine to the body. I did this while the engine was running and the engine, which had a little miss, immediately smoothed out. I took a drive. The shifting of the transmission was smoother and not winding up in rpms as in the past. The engine ran fine and had no misses. Hopefully the grounds were the issue.

I wanted to share this because when you read P1518 codes on 3.8's most never point you to what they found that worked for the repair. If this is the problem, I will keep updating this thread.