drop in mileage

this may help some one. I have a 92 sl2 and the mileage had been down for some time. There never was any code set to tell there to start. After many hours of head scratching I checked the coolent temp sensor. It was not in the 20 to 50 ohm range when warm. I set it in a cup of boiling water and rad with a digital meter. It read abput 1200 ohms. This caused the system to run in the open look as it was warming up all the time. Thus more fuel used. I changed the sensor and all is well. you can disconnect the sensor and hook up a resistor of about 100 ohms and watch the ox sensor to get back to its lean state.