many years ago i worked in a specialist tuning place that specialised in Triumph cars

the tr6 at the time had a mechanical fuel injection system.

people would regularly bring them in running terribly, and we did what we called a 10,000rpm tune up, these cars needed to be driven hard, but months of city driving gummed up the injectors and valves etc, so a hard fun around the back streets did the job, the junk that came out of the exhaust was amazing, and after 5 to 10 miles the thing would be purring, and not a spanner laid on it.

fast forward to today and the effects of varying fuel and city driving takes its toll

however electronic engine management helps to disguise the symptoms, and thats where de-carbonising can come in or the use of additives, alternatively take the car to a quite area and make it work for its keep, your car will love you

Ewen