Ok, so in the last 3 days my car has been having a rough idle, normally its at 700 rpm but its gone as low as 550rpm and as high as 1200rpm. It feels like its misfiring, just yesterday, the check engine light came on. Unfortunatly, the autozone that had a DTE scanner that could read my car just got newer scanners so now it cant read my car. The engine is a rebuilt engine with about 40k miles on it. I dont beat on my car, i get between 25 - 27mpg city. Any ideas on what the problem may be.