I just purchased on a 2003 Mazda 6s two days ago...115,000 miles on it. Purchased it cheap, previous owners stated it needed work. I have replaced the pcv valve, pcv hose, maf sensor, cleaned all connectors, checked and filled fluids, etc...it had 9 cel codes on it, either stored or new ones...one that concerned me was p0012, camshaft position timing over-retarded. after replacing the parts, the CEL lights haven't came back on after about 20 miles of driving, BUT it is still smoking pretty constantly from the exhaust, looks white to me. it also attempts to die when i come to a stop. kind of like it's running out of gas. Has new gas in it, no CEL's, good battery, new parts, etc...it's stumping me. I have a couple ideas, but i figured with it being my first crack at a Mazda, i'd get some imput. Also, it kinda seems oil-starved to me. Ticks a little louder than I'd like, and when I open the oil-fill reservoir, it's always smoking...HELP!!!!

 

Blown head gasket, I am afraid.
You may confirm that suspicion with a leak down test: