As to just how much it might be worth to have an engine inlet tract/valves etc cleaned I know not in terms of either MPG or actual power output improvement, though I suspect engines that are used mostly in slow traffic and for short runs, as ever seem more likely to foul up more than those that spend time being driven in a more sporting manner...? (-:
These were my thoughts when I was pleasantly surprised at the level of deposits on my valves after 20K miles.
