A good cheap way to decarbon your combustion chamber is to use water. Find a way to tickle water into your intake manifold. With carburated cars, one can trickle the water straight into the carb. Peolpe with fuel injection will have to find a place to introduce the water thats after the MAF sensor. First get your vehicle up to operating temperature, then trickle water in while reving the engine. The trick is not to let the engine die. This is an age old mechanics secret. Some people trickle ATF fluid, although I don't see the reason. With water, you are basically steam cleaning the combustion chamber. The water flashes to steam in the cylinder and cleans. Warning: carbon will pour out of the exhaust and your neighbors will wonder what's wrong with your car. Anyone who has had the misfortune of repairing a blown head gasket where the coolant was leaking into the combustion chamber can attest to the cleaning power of water. Usually, the cylinder that has the leak is shiny clean, where the other cylinders have the typical carbon in them.
