car presents with P0306 and 0308, running rough; and emits tick white pungent smoke in the mornings

Car runs rough and emits smoke in the mornings and when I stop and restarts after a while. I have done some diagnostic checks with the following codes:
*f P0306
*P0308
I have replaced all 8# spark plugs. It ran smote for some days and stàrted again.
What is wrong with my engine?
Thanks
Osazuwa

I would certainly have loved to donate but I am outside of the US. I hope to get intouch on my ne t visit in May.