I have an idea off a good mechanic.some engine/decoke/egr additive to fuel cleaners do actually work, but you need to check out the temperature that they need to reach to do there bit.some fuel additives will make your car run at a higher combustion, you just need to be aware to give your car a good run in a lower gear and dont keep adding to your fuel tank all the time.i dont know if the JLM stuff is any good, but there are plenty good write ups.