A light came on in my car around 4 months ago. i was told my upstream part was going out. a few days ago my car went off while i was driving. it seemed as if it wasnt getting any gas but if i pushed the gas pedal some it was trying to start but isnt starting. also the only time it will attempt to start is when i hold down the gas pedal. they also said something about an oxygen sensor. do you think its the upstream part they told me i would be needing soon or does it sound like something else? thank you