Removed battery while replacing thermostat in my Lexus RX 330. After completion I started engine to find that my check engine light was on along with my VSC and Trac Off. Engine is also not idling correctly . I'm sure it is a computer issue but I don't know what to do. Any suggestions.

Most vehicles now-a-days come equip with an on board computer. This computer stores and records several statistics about the operation, condition, and overall health of the vehicle. When you remove the battery, this computer is reset. The results can be a loss of oil level records (when it was changed, when it needs to be changed) tire pressure defaults, etc. In addition, as the vehicle is driven, the computer makes adjustments to things like fuel injection on the engine and other active tasks to improve mileage or performance.

When you reset the computer, it reset all the data along with it. This may cause the check engine light to come on as the car no longer knows the status of certain frequently changed or replaced parts. Your traction was probably turned off either as a response to this or because it was the default for the vehicle; seek out the manual for your vehicle and it should tell you how to re-enable this feature. Lastly, the idle may seem rough because you reset the computer and it no longer provides a tailored level of fuel injection. Over time, this issue should resolve its self as the computer learns.