hello, i have been having this problem with my avensis for a while, but have finally decided to find the cause and hopefully fix it.... the problem is, as it seems, that the engine is running rich, which results in significant carbon build up on the spark plugs, and in the tail pipe. also, in the last 6 months the car has had a noticeable drop in power, accelerating is much more difficult, and often the car will stutter/***** once or twice while accelerating and then the jerking will disappear (