Hello all! I have studied (not just read) close to every subaru and non-subaru related p0021 thread. It seems that for most of these threads there are alot of possible solutions, but rarely is there conclusive ending to what really can fix this infamous code.
So here begins the tale of my FXT and her p0021.
I own a 2004 forester xt. I purchased the car with 88,000k completely bone stock with receipts for every synthetic oil change.
All was well and the car reached 100,000k so I excitedly purchased my timing belt kit from Subaru. This kit included a new:
Timing Belt Tensioner
Coolant (Not from Subaru)
Now for the timing belt install, I asked my father who was a master tech at Mercedes Benz for 30 years to help me. Mind you, he didn't actually help me...instead he completely stole my thunder and did the whole thing himself and I got to pour the coolant after it was all done. This is not a complaint at all since there were zero issues, nothing broke, it was free, and it only took him a Saturday morning to finish the whole job.
Fast forward about 15,000k. I am driving home from work and the code pops on. P0021. I drive it to the rents house and my father reads it and we are baffled. The timing is obviously on (if it wasn't the car would run like a diesel) and there is no power loss. We decide to leave the car and research a little, which brings us to...
THINGS I HAVE DONE TO TRY AND FIX THE CODE P0021:
Drained, and refilled the oil more times than I can count
Run Seafoam in the oil
Removed all banjo filter screens from oil lines
Removed, cleaned, and swapped AVCS Solenoids
Replaced Crank sensor
Replaced Cam sensor
Replaced driver's side intake Cam Gear
Checked wiring from the ECU to the solenoid
Nothing has fixed the code. The car runs like a top and never stalls and the car now has 138,000k. I get the same gas mileage as when I first purchased the car. I just recently purchased new heads that I plan on beefing up slightly and tinkering with just in case I have to pull the heads off of my car to resolve this issue. As for the engine mods done to my car:
Accessport installed after the code came up
Full exhaust (catless)
Denso Platinum spark plugs (changed about 5,000k ago)
The car only sees synthetic oil. I have used Rotella 5w-40, Motul 5w-30, Amsoil 5w-30, Valvoline 10w-30, Mobil 1 0w-40 (only once) and now Castrol 0w-30. Mainly I have stuck to Rotella and Amsoil. I change the oil every 3,000k and sometimes sooner and I don't burn oil.
The reason I am writing this extensive post is to gather as much information on this code as possible and to hear all of your experiences. I have seen the issue be something as small as a oil supply screen, all the way up to starved turbo. My car falls somewhere in the middle of that and I'm sure lots of other subies do as well. If anyone has any questions or comments please feel free to post!
Thank you everyone!