sudden drop in gas mileage

1996 SL2, 200'000 miles. A few months ago soaked rings per 'saturnfans forum" post to cure excessive oil consumption; it did not work but fuel consumption went from 38 MPG to 25 MPG! Plugs are black, front O2 sensor reports LEAN, code for intermittent misfire, check engine light on. Replaced plugs & wires, O2 sensor, coil pack (measured open but still ran fine),MAP sensor, and PVC valve with no change. What is next?

 

Coolant temp sensors are a common failure point on these cars. Unplug the sensor and look at the pins in the connector. If they are green replace the temp sensor and pigtail connector.
The fuel mileage is directly affected when these fail. Also will cause hard start and smoking.

 

Thanks, I had forgotten that I did replace the coolant sensor with no change but did not check the pigtail. Is this the same sensor that drives the temp gauge (the gauge still reads normally) or is there another one; I have seen some references to two different sensors on some models but I find only one on mine?