my car is idlling so fast that it dosn't want to change gears?

Paula ...... one thing you can do is to disconnect the battery for at least 30 minutes bearing in mind you will need to re-enter your Radio code when the battery has been re-connected. This will hopefully reset the "learnt" settings stored within the ECU. Why did your son change the O2 sensor? Another possible reason is the Idle Control Valve could be sticking and sending incorrect information to the ECU. This can be cleaned by using a carb cleaner sprayed into the ICV.

Chris
February 2008