A flashing check engine light indicates a misfire while the car is running. You will want to check your ignition components such as the plugs and wires. You may have a spark plug that is fouling and this would cause the light to flash.
You also want to check the distributor cap and rotor as well as the ignition control module.
A great test to this would be a spark test. If is any of the plugs are misfiring at the wires, if no misfire present you will want to change the spark plugs.