I have an 04/04 built Optima and I have having the exact same problem as the first posting.
I am a mechanic and this whole thing is driving me CRAZY! I have the code tester and have been dealing with this for about 3 wks now. I was getting NO CODES until just yesterday.
So all this led me to believe I was having a fuel related problem. Which the killer is, I changed out the fuel pump (very easy) and then drove the car over 50 miles w/o single problem. ALL GOOD! Nope! It started acting up again. Same issues, only thing this time, I finally got the code PO335.
The FUNNY thing is.............................I just spoke w/ a Kia Service Tech and acting as if I don't know anything about cars, he did tell me that the Crank Sensor HAS BEEN KNOWN to kill the car w/o popping a code. It is a VERY crazy thing that the Crank Sensor (a completely electrical part with NO MOVING PARTS!) can do that.
So, now I am going to have to buy a crank sensor and replace it. While I am at it, I will do the timing belt and get it all done. Just can't do it till Feb 15th.
While doing the work, I will take pictures and document the work. That way, anyone who wants to do it themselves, I will provide you the info, you will be able to do it yourself without having to pay all that labor.
I'll keep you all posted when I do this.