I have a 2004 chevy classic. At first my engine light was on and i got the O2 sensor fixed at chevy dealership and then it went off. It came back on the next day. I took it back to Chevy dealership and they held it for a day and told me that it was a wire that they fixed. No signs of engine issues they said. The check engine light was off but i still had a rough idle at a stop or when im reversing. I got the spark plugs replaced but it didn't fix the problem so i replaced the air filter but car still had bad vibrations. Thought about it being my brakes so i got the rear brakes completely done, the fronts still need pads and calibers. Guy told me the brakes has nothing to do with the vibrations at a stop or in reverse only when braking. About four days after the second visit from chevy the engine light came back on, i went to AutoZone to get the engine light checked out and got a PO455 code. Which indicates a leak in the evap or no flow. Im going back to the dealership on monday but i also tried to replace the fuel cap and clean the injectors by putting a 16 oz of seafoam in the gas tank that was 1/4 filed and then add more gas til it reached 1/2 a tank. Now i hear a noise that happens when im accelerating that sounds like a bad scraping or metal screeching im not sure. I don't know what this problem can be and i don't want to keep wasting money.