cleaning out the intake manifold

Most likely you will never need to do this, but if you live in a dusty area it is a good idea to check and do the following if necessary. If you see built up deposits of gunky looking "mud" or a greaselike gunk in the throttle body and intake manifold, it should be cleaned. Ford recommends not doing this because they have coated those inner portions with a special coat to prevent such buildup. Apparently it doesn't work so well, so you must clean it. To do so is simple. Unbolt the throttle body. This exposes the inner portion of the throttle body and intake manifold. Spray liberally with throttle body cleaner and let it soak. You can go nuts on the throttle body since it'll just run off. After the TB (throttle body) is cleaned and the intake manifold is sprayed, bolt the TB back onto the manifold. Start the engine and spray the carb cleaner into the TB when the plate is open. Open the butterfly plate (disc plate in TB to control air) in short bursts to prevent over revving the engine and let the engine pull in the throttle body cleaner. This will spread the cleaner through the runners of the manifold and clean off the top of the intake valves. Make sure to use a cleaner that is safe for injectors and O2 sensors.

The PCV valve is designed to suck crankcase vapors from the crankcase into the intake manifold and burn them with the fuel mixture so that they don't pollute the environment. In high mileage engines the crankcase vapors are increased due to excessive blow-by. Therefore there are a lot more vapors and general oily junk that are sucked into the intake manifold. On carbureted engines this junk is continuously flushed away by the gas vapors which have lots of good detergent properties if you are using a decent fuel. Therefore there is no build-up of oily carbonized residue in the intake manifold.. On the other hand, fuel injected engines introduce the gasoline way down by the intake valves and there is no gasoline inside the intake manifold "above" the injection point and thus nothing to flush away the crud that builds up inside the intake manifold around the place where the PCV Valve dumps all of its garbage!

The result is a gradual build-up of thick oily carbonized material that eventually chokes an engine until it will no longer perform the way it used to. Introducing "in-the-tank" cleaning agents like Gumout etc. can do nothing since the fuel never reaches the region where the crankcase garbage build-up occurs.

You can remove the throttle body and peer into the intake manifold to see if you can see the area where the PCV tube does the damage to see if there is a problem however I advocate just removing the tube from the intake manifold and introducing carburetor cleaner into the port. The engine will run very poorly with the tube removed completely however if you restrict the opening so that it is only the size of a pencil lead then you can stick the nozzle of a can of carb cleaner into the hole with the engine running at a fast idle and squirt the cleaner into the opening.

You need to do this slowly since the release of all that buildup can choke an engine to death so give a squirt, rev it up a bit and then give another squirt. It is possible to remove too much at a time and foul the spark plugs so do it slowly. You should see a noticeable amount of smoke coming out of the tailpipe unless the catalytic converter is very thorough in doing its thing in burning up the smoke.

When you are finished you should see improved performance and better gas mileage. If the junk is too carbonized from being on there too long then there is nothing short of removal of the glop by brute force means like the sharp end of a long chisel and a vacuum hose to suck out all the mess that you loosen up. Sometimes it is necessary to remove the intake manifold to remove all of the residue.

i used seafoam carbon cleaner on my sisters civic ex
i followed the directions from the SHO how-tos bak in the day
about the same as the ones viper posted

I just unplugged the hose and turned on the engine and put the seafoam in a lil cap since the seamfoam isnt a spray,
and i let the engine suck it up, the idle was kind've crazy since the air/fuel ratio was mostly fuel wit little air, so my dad was giving it gas to keep the engine alive, after it sucked enough, i shut off the engine and let it sit for 5 minutes to dissolve all the carbon deposits, at that time i put those bak together and cleaned up the spilled cleaner

then i looked up and was shocked at the huuuuge!!!! cloud of smoke in the distance, it was caused from the engine burning some carbon cleaner

well after 5 min i started it up and went for a drive as instructed in the directions, u have to drive it till smoke stops coming out of your mufflers

well when i drove it i would leave clouds of smoke behind, the burnt carbon, i drove it for 5-10 minutes till it stopped smoking
i still remeber that day cause i got a ticket shortly after it stopped smoking because i didnt stop fully at a stopsign, what bull shit

it looks crazy when ur leaving clouds of white smoke behind you!!
heres a pic