Installed a jdm engine in 2010 Forester, with usdm heads and intake. Starts right up and seems to run smooth, but have a P0026 and P0028 code. Also have a PO198 for oil temp sensor. I'm at a loss on what could be wrong and how to trouble shoot the problem.

ive had a kinda similar problem. i would get p1512, p1514 and p1516 codes and what it had to do with it, was it had to do with my iac valve. I found what helped me was i cleaned the the sensor with some maf cleaner (or you could use any sensor cleaner), after that i cleaned the the wire and connector with contact cleaner. Then after i reset my ecu and everything was fixed.