The other day my CEL came on. It threw a code P0125: Closed Loop Fuel Control, Insufficient Coolant Temperature. I had it scanned at Advance. They said I needed to replace my coolant temperature sensor. So I bought one and changed it out. The CEL went off immediately, for a few days, but today, it came on again. Advance scanned it again, same damn code. Now they are saying that maybe my coolant is not reaching proper operating temperature. I HAVE noticed that my gauge reads quite a bit cooler lately than it used to. I know that the stock gauges suck, but it's a significant difference. I'm not sure if my coolant/water mixture is bad or if its a bad thermostat, or what. I'm thinking about flushing the coolant to start off. What do you guys think? Any ideas?