My engine is running rough. It seems fine in park. When the car is in drive it rocks lightly front to back. There is a slight rough rattle coming from under the hood. I made the mistake of putting in some pretty crummy gas about two days ago and this started about 3 hours later. The last time I took it to have the codes read, I was told the place by the pedals that the machine hooks up to did not work. Is there some way to test this with out the code reading device?Please advise.