Q: The codes p0012 and p0015 was shown on the scanner when I had my car checked.

I'm troubleshooting. The engine has begun to fluctuate in rpms occasionally with idle, and generally after driving long periods and coming to a stop. The car would always jerk a little after coming to a stop since purchase, which I never thought much of, but has led me to believe it may be timing related, either mechanical timing or loss of pressure due to a deteriorating head gasket or leaking VVT system. The initial issue was an engine misfire on cylinder 3. This was corrected after driving for some time by replacing the coil pack on that cylinder. In the month or 2 following, drove fine. I still havent replaced the rest of the coil packs/spark plugs. After getting the p0012 and p0015 codes recently I replaced both Vanos solenoids which resulted in a better driving experience for maybe a week. I also noticed the oil fill cap was leaking and replaced this. I'm wondering if oil cap leak could be related to head gasket or VVT, because still appears to be an issue, codes keep coming back

My car has 144000 miles.
My car has an automatic transmission.