Hyundai Repair: check engine light, obd ii code reader, obd ii code

Question
QUESTION: light flashes on and off and sometimes it will be on steady

when the car moves from a stop it vibrates and sounds very rough but as you increase speed it runs smooth

2003 accent with 59000 miles
ANSWER: A flashing check engine lamp indicates a misfire that's severe enough that it could damage the catalytic converter.  If you're able to read the trouble code, the code will tell you which cylinder is misfiring.  Misfire codes are in the form P03xx where xx represents the misfiring cylinder.  For example, if you had a misfire on cylinder number 2, your trouble code would be P0302.  P0300 indicates a misfire on more than one cylinder.

Most misfires are caused by secondary ignition component (spark plugs, plug wires, ignition coil) failures, so I'd recommend checking those items first.  If you know which cylinder is misfiring, it'll make your diagnosis shorter and easier.

---------- FOLLOW-UP ----------

QUESTION: where do read these codes ?  

Answer
You'll need an OBD-II code reader to read the trouble codes.  Many parts stores and Sears sell them.  Also, AutoZone and AAMCO have advertised they'll check your trouble codes for free, but since your check engine lamp is flashing, I don't recommend driving the vehicle.