I'm working on getting my "new" beater 98 Cavalier 2.2 auto tuned up for a daily driver. I got the engine codes read at AutoZone, and the guy said it was the TPS, IAT, and O2 sensors but he couldn't tell me whether they were high or low, or give me the actual codes for them..? That's about all I can get because I don't have a real GM dealership anywhere nearby.

I'm not familiar with this engine, but it's an interesting code combination. Is the intake air temp causing the engine to run rich/lean and causing a good O2 sensor to read this condition? Is the TPS completely independant of these other problems?

It sounds to me like the guy at AutoZone wants to sell you a TPS, an IAT, and a couple of O2 Sensors. What kind of scanner doesn't tell you the codes? Total bs, IMPO.

Well the car seems pretty slow, doesn't get the best mileage, and uh... oh, it has a check engine light on, which wouldn't be there if they were only trying to sell me stuff for no reason.

The TPS & IAT are not that expensive, the IAT will tell the ECM to advance or retard the ignition spark somewhat according to the inlet temp. (I know the knock sensor does that as well on a sense of knock) The TPS may have a "dead" spot in it, but that's hard to tell unless you hookup a scan took or ohm-meter and watch it as you cycle it from idle to WOT. If it's the manifold O2 that will cause rich/lean depending upon how it's acting. Food for thought.
Don