Currently working on a 2008 A4 2.0t 6MT that had an oil pump failure at 74kmi. I swapped in a low mileage 2006 motor and have been having constant issues. The car barely ran when I first did the job, but I narrowed that down to the PCV. Swapped that out, ran great but had no boost whatsoever and had code p0299, but nothing else. I drove the car for maybe 300 miles and still came up with no other codes. The wastegate ended up being shot in the turbo on the new motor, so I swapped the old turbo in and have had no other issues with boost or the p0299 code. But after 65-70 miles of driving, the CEL pops back on with p2096: Post Catalytic Fuel Trim System Too lean. So I figured I would space the secondary o2 out to see if that helped, which it did, but now after the same 65ish miles of driving I'm getting p2196 for o2 sensor 1 stuck rich. I changed out both o2 sensors when I replaced the motor so they are brand new, but I swapped the old primary o2 back in just to see if that would make any difference. It didn't, after another 65 miles the CEL popped back on for the same code. I did a bit of research which suggested a possible evap leak but I don't know. I tried using a smoker to test for leaks but I'm not sure of the best place to test through as there is no evap service port on these cars that I'm aware of. If anyone has any suggestions they would be greatly appreciated. Thanks, Dan.