1998 Chevy Malibu Engine light flashing, code 302

I have a Malibu that was just put in the garage because she was hard to start. At first she turn over and over but not catch. Then all I got was clicking then nothing. We tried to boost but seemed like we were not getting good connection. We decided to have her towed to the garage.I had new Spark plugs and wires installed and the battery charged. She now starts but the engine sputters and shakes the engine light flashes and she even has a poor smell from the exhaust. She sputtering and shaking that bad that we cannot drive it. With so many kms I am not looking at spending a lot of money if this is something big. The garage said she is showing engine code 302 but was not exactly sure what the problem would be. ( The garage just does maintenance) Please give any advise as to what the problem could be. Thanks