My wife bought a 2000 Dodge neon from a used car lot about a month ago.The car ran fine until yesterday.She checked the oil and it was low so she added some.When she did the check engine light came on.The car now lopes and acts as if its going to stall.She had dianostic ran it came back (plug no.2 misfiring).She took it to a shop and they checked and said that was not the problem.What do you think the problem is?