the engine cleaner they say cleans the carbon off the engine and gives better fuel economy.Is this true?
Can you do it yourself easily?
It depends on the engine. If you have gasoline direct injection, using an upper engine cleaner every 30K miles can reduce carbon buildup on the valves. If you don't have direct injection and the engine isn't having any problems, it's a total waste of money. See this post on what the problem is with direct injection and how to do it yourself
