There are a number of compounds used to remove carbon deposits from the cylinders and inside the heads of engines. Recommendations on what to use and how often vary. I have used RedLine “Fuel System Cleaner” with excellent results. I was astonished at the amount of crud that was blown out of the engine, as well as the engine idling better and running a tad cooler afterwards. If this has never been done, or even not done in 20K miles, you won’t be disappointed at the difference made. Generally you put in the treatment, fill up the gas tank and then burn up the tank on the freeway or other spirited drive. I like to drive to the mountains. At some point their will be a near mushroom cloud of debris to exit the tail pipe. That’s the carbon buildup getting blown out. The common wisdom is to change your oil right after running this tank of gas through the system as at least some of the deposits end up as particulate matter in the oil system.
'00 ML320 "Casper"
'92 400E "Stella"