I think that the absolute best stuff is the Mopar combustion chamber cleaner. This stuff is 70% water, and uses amonia for the cleaning agent. Warm the engine up real good, and just spray it down the throttle plates and into the idle air passages with the motor running at idle. It will want to run rough, and move the idle air control out and in, which helps get a better cleaning action. As it goes into the combustion chamber, it will turn to steam, and clean off any carbon and olifins that accumulate. When the can is about 3/4 empty, shut off the key, and fill the throttle plates to the top to soak for about 5 minutes. Now spray some more down the throttle and scrub it with your fingers. Then start the engine, and run the rest of the can through. RE-attach the air cleaner and drive it down the highway until it quits smoking.
This stuff is great! It will raise compression by freeing up rings, and will also cure the carbon knock that is assocoiated with high mileage 4.0's and 4.2's.
One other thing. It will not carbon foul plugs, as normal carb cleaner will. You should never do this with carb cleaner!
