code - 76 engine running rough left side

[waffles666]

Hi i recently purchased a VS 3.8L ecotech and it has developed some funny noises and lost heaps of power. The left side of the engine will make like a sucking/rattling noise although that is a very bad description it just sounds like the engine isn't firing properly I checked the flash codes and it came up with a 76 which is petrol/air mix not the same on both sides of the engine which is certainly what it feels like. It basicly feels like at high revs that the right side of the engine is just pulling the left along for the ride but even when i cant hear the noise it feels like it has lost a lot of power. I reset the computer by disconnecting the battrey and the code hasn't come back but the issue is still there. Any help would be much appreciated but i will be taking it into the mechanic asap as the noise is getting worse.