So the check engine light came on in my '89 740 (211K), and my mechanic diagnosed a bad O2 sensor, which he replaced (and I saw it ... it needed replacing). But then a few days later the light came back on. He's says he not getting the 02 sensor code anymore (good), but he getting codes (and I don't know the numbers) for the NOx and the Throttle Position sensors. He says that it would cost a few hundred bucks to replace them both, but that likely only one would need replacing, since one being bad would likely give both codes.

So my questions: (1) does this make sense? (2) did he say "TP sensor" or "TP switch" ... I can't find reference to at TP sensor in the FAQ, (3) I'm thinking that I might just replace them both myself, and save a few $$$ ... good idea? (4) if the answer to #3 is "yes", could someone point me to the FAQ -- or another resource -- that would be instructive? I can't seem to find anything on the site ...

Thanks, all.

TPM