I agree to run codes first, but bad O2's won't show up on a code scanner (unless they are unplugged or WAY bad). I think it would be smarter to replace the O2's before the MAP because as was mentioned, the O2's are ignored for the first 2 minutes of EVERY startup. The MAP is always read. Plus, O2's are notoriously going bad with about 80k miles on the clock, if not sooner.