I have a 2000 Hyundai Elantra. Well the thing was running fine although using more gas the normal until today. As I was going down the road and stopped at a red light it started jerking really bad like it was trying to go. Then all of a sudden while driving it started shaking and jerking and the check engine light came on. My step-dad checked all the fluids there fine and we even replaced the spark plugs because it sounds like it is missing and having trouble catching when you first start it or when your stopped at a light. I took it to Advance but they cant test it because their machine hook-ups wont fit on my car. (whatever that means?) I was told it could be the coilpack or the oxygen sensor how can I find out for sure what is wrong with this car????? Thanks for helping me!!