Ohio4Runner

Hello all. My 2005 Sequoia Limited is throwing all 3 codes at once: p0031, p0051, p1316. I have changed both upstream O2 sensors, changed the spark plugs, bought a new gas cap, and checked the MAF sensor (works) and air filter (fine). Erased the codes, and the errors came right back (although the idle is slightly better than before).

Any ideas where to look next? I guess I could get into the secondary air injection system, or the camshaft timing oil control sensors, but probably someone here has a better idea.

Thanks.