I tightened loose intake bolts, cleaned the MAF with CFC brake cleaner (the real stuff in the red can that's nasty, not the environmental stuff in the green can that leaves a residue), and cleaned and made sure all hose connections on intake were tight. P1158 cleared and has not come back in 8k miles. Plenty of other stuff with this maintenance pig, but not that (knock wood). I think it was the intake bolts and that tightening them back up it finally resealed. They're easy to get to with a small (1/4" drive) 10mm deep socket and extension; five on each side. Never did change the 02 sensors, they weren't the problem.