Had the code (P0021) show up on my '05 XT Outback. I'm the only owner and performed all oil changes per the recommended (and updated) maintenance schedule. Given how relatively inexpensive they were and the success found by some, I replaced both OCVs. That seemed to help for ~400 miles but the code returned after a long road-trip.
I'm not confident enough in my own skill to pull the banjo filters but that might be the next step.
Question: Could someone explain how to read the Intake OCV and VVT data? Can your standard ODBII dongle + software do the trick?