2002 Oldsmobile Other Repair Question
if you can pull a code, that would be helpful. Also, there could be a 1 wire or 2 wire O2 sensor.
If the O2 sensor is bad, it could effect the dwell and the Mixture Control Solenoid. the MC solenoid controls carburator feedback system to maintain Air/Fuel Mixture. This solenoid on-time (dwell) is controlled by the PCM based on inputs from O2 sensor, Vacuum switches, ECT, IAT, and vehicle speed. If you have a replacement O2 sensor and no way to test the existing one, Make sure the harness plug supplies 450mV reference signal from the PCM to the O2 sensor. If it does, swap them and see if it helps. That would be a quick test. Otherwise, you should get the code(s) that tripped the MIL light on and go from there. Dueling the exhaust, (Although may be a federal no-no) shouldn't effect the fuel economy negatively. With the miles on the vehicle, it could be a multitude of things including EGR, the carburator itself, internal engine component wear, etc... you need
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