1997 Pontiac Firebird

If you have more than 100,000 miles, check the o2 sensors with a scan tool that reads live sensor data, also check the ECT(engine coolant temp sensor. Did you put a K & N air filter on this by any chance?

Many sensors can be slightly out of normal range and not set a code, Crank sensor O2 sensors ECT...Test them like this:
CRANKSHAFT POSITION SENSOR A malfunction in the crankshaft position sensor circuit will set a related diagnostic trouble code. For testing procedures, see the TESTS W/CODES - 5.7L article. To diagnose crankshaft position sensor, the following procedures can be used: 1. If a scan tool is available, scan RPM parameter while cranking engine. If RPM is indicated, crankshaft position sensor is operating properly. 2. If scan tool is not available, disconnect crankshaft position sensor harness connector. Set ohmmeter to 2-k/ohm position, and measure resistance across sensor terminals. Resistance should be 800-1200 ohms. 3. On all engines, set voltmeter on the 2-volt AC scale. Crank engine and measure output voltage across sensor terminals. Voltmeter reading should be .8-1.4 volts. If resistance reading is not as specified or sensor does not produce the specified output voltage reading, repair faulty wiring or faulty crankshaft position sensor. ENGINE COOLANT TEMPERATURE (ECT) SENSOR If a coolant sensor-related diagnostic trouble code is present, see the TESTS W/CODES - 5.7L article. An out-of-calibration sensor may not set a diagnostic trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See ECT SENSOR RESISTANCE VALUES table.

Also if you can scan the MAF while running it should read 159 hz at sea level.