My 2004 Pathfinder began running terrible. It felt like I was towing a ton of bricks. Finally got off the highway and took the back roads home because I couldn’t get it over 40MPH. I attached my code reader and it showed P0021. Internet research showed words like Oil Viscosity, Oil dirty, Stuck, Seized timing valve.
So I took a chance that the VVT has affected in some way by my oil. I added about 12 ounces of Marvel Mystery Oil and let it idle for 20 minutes. It was fixed. My test drive showed the engine was back to normal. I suspect the timing was off due to oil viscosity since I am my own worse enemy when it comes to additives.
Anyway I hope this could help someone else who may encounter a P0021 or P0011 issue. Thanks, this is a great forum. Hope I added something useful.