2006 Kia Rio CEL on and Running poor.

What is your question?

Check Engine Light is on and occasionally flashes when accelerating. OBDII Codes were "Cylinders 1 & 4 Misfiring" I changed all plugs...still happening. Cylinders 1 & 4 missing during accelleration and in general. Any ideas??? I read that this happens alot but have not seen an answer anywhere. Thanks in advance, :-)