If the car has milage over 175,000 with the origional fuel injectors I am sure this is the problem. I have a lumina with 333,333 and every 175,000 I have to replace all the fuel injectors. Then all those codes will disapear and the car will run great for another 175,000. You can purchase a set of six fuel injectors from Summit Racing out of Talmage, OH. The brand is Accell. Make sure you by the stock version. If you buy injectors at the autoparts store they will cost you $50 each for an off brand or rebuilt or $100 for Borg Warner. I would check the fuel pressure and other obvious stuff, like using a good brand fuel injector cleaner but if you have the orgional injectors and the care has around 175,000 it should be the fuel injectors. Been there done that replaced the same stuff you did and have the T-Shirt or two!