Intake Manifold Carbon Build Up?

[bobcowan]

A certain amount of that is pretty normal. Standard tune up procedures for modern cars include cleaning the carbon out of the throttle body.

[FWB]

do you have a pcv plumbed into the intake plenum?

[olddog]

Originally Posted by FWB

do you have a pcv plumbed into the intake plenum?

Yes at the base of the throttle body, pretty much like a carb would be.

[FWB]

that is where your oil residue is coming from. is there a baffle where you pull the pcv from the crankcase? if it's from the valve cover you might be sucking raw oil into the plenum.

there isn't a trick to cleaning it, because if its that way in the runners the backs of the valves prolly look worse. when the oil mist hits the hot valve , it immediately crystallizes on the back of the valve. i would pull off the intake to clean it, and then it will give you the ability to see what the intake valve looks like

[Mr Jody]

I ran into a similar situation recently, and have one trick you may want to try before pulling the manifold. I am in the process of replacing fuel injectors on an old Nissan Maxima and saw the same oily, gritty residue inside the manifold, which I attributed to the flow of oil vapors through the PCV, but at 160k miles this should not have been a surprise. I knew I wouldn’t be able to get it squeaky clean without taking it off of the engine, but I did want to clean the bunghole area for each injector and any other places I could get to that appeared to have excessive buildup. I could see the back side of the intake valves through the bungholes and they actually were surprisingly clean.

To avoid having any residue I scraped off end up on the valves and subsequently into the cylinders, I took my shop vac, attached the crevice tool to the suction hose, and then stuck a piece of clear rubber hose (about a foot long and small enough to fit into the bungholes) into the crevice tool and wrapped tape around it at the crevice tool to hold it in place and close up gaps in the crevice tool opening around the hose.

After scraping inside each bunghole I would then suction out the residue either through the bunghole or the intake runner. The intake manifold on this car is made in three sections stacked on top of each other. To gain access to the injectors you have to remove the top two sections. This actually opens up each intake runner and helps in being able to gain access to other areas of the manifold, which may be more difficult in the one piece manifold of your engine. But the suction of the shop vac did remove residue that I was scraping off that ended up on the backside of the valves.

In your case, you may not be pulling the injectors, but maybe you can use the suction trick to remove what residue you can get to through the top of the manifold.

I would NOT recommend this method in conjunction with use of a volatile cleaner for fear of the vapors passing through the electric motor of the vacuum and potential sparks in the motor not playing well together.

[wrogers55]

While you are at it, have a close look at the mass-flow meter on your system. If the manifold is that bad, you have another bigger problem. Three little, really little, wires across the air inlet of your mass flow meter. If they are coated with "anything", the meter will report bad information to the computer. The result is usually very poor fuel milage and poor throttle response, at the least. Clean them without touching them if at all possible and only with something made for the purpose. Brake clean or carb cleaners will likely leave a residue on the wires and cause the same problem. In the worst case use a stream of isopropyl alcohol, better case is a spray can of cleaner made specifically for the purpose from the auto parts store. Don't break the wires cleaning them....$350 or more to replace that little jewel.

I'm not that smart, just lived through total frustration with this exact problem once upon a time........