92 Olds Speedometer pegged/Running ROUGH!

I have a 92 Olds Silhouette with the 3.8l engine. As my wife was driving the car, it cut off and wouldn’t restart. When I got there to check on the car I found that the speedometer was pegged all the way around and the car wouldn’t start. I had the car towed home. I checked the diagnostic codes and it give me a 14 - which is the coolant temp sensor. I replaced the sensor and then tried to start. The car now starts but runs really rough, and cuts off immediately when I take my foot off the gas. The speedo is still pegged. Whatever pegged the speedo is probably what is causing the car to run so rough. Any help is much appreciated.

:banghead: