1993 Pontiac Firebird Rough idle, bad gas milage, engine co

That is too many codes to be accurate. Erase the codes and drive around for one or two complete heat cycles, or a day or two. Then post back and lets see what codes come back.

Check EVERY ground. Make sure they are good and clean -- also, measure the resistance to ground. It seems that many of the sensors that the trouble codes indicate, share the same ground. Also, Make sure that the battery ground (negitive wire) is clean and terminated to the chassy good and clean. Your check engine light may be burned out. Test to see of there is voltage to it -- if there is then check the ground to the ECM again. Your ECM applies a ground to the check engine light to trigger it. If the ground to the ECM is bad then it has no way to illuminate the light. Just because a sensor has voltage does not mean that the sensor is working properly. Many sensors rely on a good ground termination to operate correctly. Your manual should have a ground distribution diagram that informs you on where to look for the terminations. If you are sure that all the grounds are good, then try removing power to the ECM for 5 minutes. Then try to erase the codes and see what comes back. If this fails then have the ECM reflashed at a dealer. If this fails then it could be the ECM. But it is rare that an ECM of this year fails.
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