2007 Saturn Ion 2007 Saturn Ion Missfires

I own a 2007 Saturn Ion, lately it has been registering missfires, especially when it is low on fuel. I usually put Arco gas in it, but purchased one tank of 76 gas in while on vacation back in mid October. Shortly thereafter, the engine light came on and stayed on and it registered 3 missfires on my Actron code reader. I have already used two cans of a product to clean my gas tank, and the problem seemed to get a little better, but then I got a warning light on the far right of my dashboard, that looked like an engine symbol with an arrow pointing down. HELP. PLEASE. 2 more years of payments on a car that is basically now a planter!