1998 Saturn SL1 1998 Saturn Engine Cranks won't Start

Hi, I actually had this problem before, I thought I fixed it when I had a 90,000k tune up at the dealership 3 months ago. Usually the engine starts fine most of the time, but just yesterday night the engine started but died. It took me around 15 mins cranking the engine between breaks for the engine to start again. I know it is not the battery, spark plugs were replaced, had new fuel injectors, fuel pump is fine, I had the engine diagnosed during the tune-up. The only thing I did not fix was a faulty O2 sensor, which could it be the problem? Also on a few occasions when the engine starts okay, sometimes when I switch to reverse or tap lightly on the gas pedal the engine stalls a bit and goes back normally.