In my observations from the past few weeks (since I've had my carbon cleaning), I have noticed much better fuel economy (back to when it was new) and the car pulls much better. This is especially noticeable at higher speeds when overtaking vehicles. May not be enough reason for everyone to do a cleaning-- but I really am enjoying the way the car is pulling now.


so to Blitzzer's question, I would say the common symptoms are lower fuel economy and weaker throttle response. Since this is a gradual buildup of carbon, the loss is also gradual, and goes unnoticed.