Why my car cranks but wont start, but once started engine idles rough, and when step on gas engine dies?

93 toyota camry. 4 cyl. engine. In the past two weeks I have had a tune up, oil change, all fluids full and good, fuel injection cleaner, and fuel filter. Its strange how car starts up fine and rides good one day, and then the next day it cranks, but wont start. After many attempts it will start, but idles rough, then when u step on the gas,the engine dies. My check engine light is on, but mechanic diagnose code and said code was faulty airbag. I need my car fix, but dont know where to start, well i know its not the engine b/c it had spark, i did get a tune up, so what could be the problem?