I have a 2002 Ram 1500 with a 4.7 in it. I have code P0031 coming up for about 3 weeks. When the weather was cooler it ran fine. We just got hit with close to 100* weather and my truck is running really rough. Any Ideas.

 

Bank 1, sensor 1 (pre-cat O2 on drivers side) heater failure. You either have wiring issues, or the O2 sensor is bad. This will have a rather negative affect on fuel economy..... Check the wiring, if the wiring is good, replace the sensor.