Check Engine Light blinking on 2005 Subaru Baja

My check engine light went on and I took it to subaru to see what it was. They said O2 sensor. I fixed it and a week later check engine light back on. Brought it back and I was told it needed a tuneup, now tuneup didn't fix it. Car idles rough, hesitates, and check engine light is blinking. Any ideas?

Asked by for the 2005 Subaru Baja
wires and coil may have to be replaced as well. i do that as part of a tune up

1 more answer
Go to an auto parts store and borrow their code reader so you can get the specific code it's throwing and report it back here. That will help with diagnosis.