Carbon build up in intake manifold

[325is_e30]

what would cause black carbon to build up in my intake manifold. It was also on my intake valves and around the injector nozzles. This caused my car to run terrible until i switched manifolds. I am worried that i did not fix the casue of the problem
any help appreciated

[EverWiser]

Someone else may have a better answer and this may not apply to your particular car, but if your timing were too far advanced your intake valves could have been opening before all of the exhaust gases have escaped. This could cause some of the exhaust gases to be forced into the intake before the piston starts on its way down to pull in the next intake charge. I think this could cause the build up you describe. I'm sure there's numerous other possibilities but that's the first thing that popped into my little head.

[325is_e30]

yeah its a good idea but i had it adjusted allready when looking for problems

[EverWiser]

Another possibility would be the accumulation around the intake valves is preventing the valves from sealing properly and allowing some of the "smut" back into the intake. Have you compression checked the engine? Is it idling roughly or does the exhaust smell rich? Have you changed the O2 sensor since you've had the car? Sorry for all the questions...Just throwing some stuff out there...

[Digitalwave]

It happens because the crank-case gasses are vacuumed and sucked back through the intake manifold for emissions purposes. The best way to stop it seems to be to route the gasses into a catch can instead of back into the manifold.

[325is_e30]

I compression tested every cylinder and each was at 150psi. I have a new o2 sensor ready to go in and new injectors waiting also.
Digitalwave- Is that an EGR valve? Do these cars have one or what. Any write ups/ info on blocking it off or re-routing it??
Thanks

[RedBaron86325]

It happens because the crank-case gasses are vacuumed and sucked back through the intake manifold for emissions purposes. The best way to stop it seems to be to route the gasses into a catch can instead of back into the manifold.

I am testing a new product which takes care of that. It actually filters the crankcase air via a liquid filtering media before going back through the intake.

[george graves]

search for "seafoam"....