How to Clean Carbon Out of an Intake Manifold

by Richard Rowe

As the basis for all life on Earth, carbon is great stuff -- in your engine, not so much. Ironically, the carbon deposits in your engine actually come from previous life on Earth, in the form of the dinosaurs you're burning the keep the vehicle running. Perhaps it's fitting that bits of them decide to hang on in your intake for one last moment, before getting sucked into the maelstrom of combustion. But, sympathy aside, they do have an awful way of gumming up air passages and costing horsepower. And that's the part that counts.

Step 1

Locate the vacuum hose leading directly from your intake manifold to the brake master cylinder booster. You can trace the vacuum hose from the booster to the engine to make sure there's no junctions or sensors in the line. Unplug the vacuum hose from the brake booster or the intake side of the hose.

Step 2

Plug one end of your vacuum line adapter into the vacuum hose you just pulled off; plug an 18-inch length of 1/4-inch vacuum line onto the other end of the adapter. Pour about 8 ounces of engine cleaner -- about half the standard can -- into your plastic bottle or glass jar. Drop the other end of the 1/4-inch vacuum hose into the bottle. Carefully hold the end of the hose just above the top of the liquid.

Step 3

Have your assistant start the vehicle. Expect it to start and idle rough, since you've opened up a sizable vacuum leak. Have your assistant hold the throttle at about 2,000 rpm -- no higher.

Step 4

Start lightly dipping the end of the tube down into the engine cleaner so the engine is just taking little "sips" -- just one little sip every two seconds or so. You'll hear the engine bog down, and you'll see it start to spew black or white smoke out the exhaust. Don't be alarmed, this is completely normal, and it's not hurting the engine. This is just a result of the engine running very rich, and not completely burning the cleaner.

Step 5

Continue doing this until you've got about 1 ounce of fluid left in the bottom of your bottle. It should take about a minute. When you're down to the last ounce, completely submerge the tube for a full three seconds, and then have your assistant immediately shut the engine off if it doesn't stall while it's pulling in that last slug of cleaner. Again, don't be alarmed. Stalling is normal here. But this part is important, because it give the heavier deposits a good, wet douse of cleaner that will soak in and break them down.

Step 6

Wait for at least 30 minutes, so the cleaner has time to break down the carbon deposits. Pour the remainder of the cleaner from your can into the bottle. Start the engine back up, and repeat steps 3 through 6, until the last of the cleaner in the bottle is gone. Unplug the vacuum line from the fitting, and plug it back into the brake booster.

Step 7

Pour half of your second can of cleaner into the gas tank, and then top up the gas tank with a "Top Tier" gasoline. You can find Top Tier retailers in the Resources section below. These premium gasolines contain high-grade detergents that will work well with the engine cleaner to rid your engine of existing deposits. Continue to run at least one tank a month of Top Tier gasoline to keep your engine clean and free of carbon. In between, add a couple ounces of your remaining engine cleaner to each tank, until you run out.

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