The early models don't seem to have the problem it's the later euro vehicles that do. What model vehicle is he testing on, would like to know. I have found If I am away and towing there is little to no build up in the electronic throttle body, but when at home doing short trips this causes a build of sludge up vey quickly. So before I do a trip I remove the electronic throttle body give it a clean and it's right for the trip.
Cheers

