Quote:
Originally Posted by Mxfrank
And now you have a car that emits more NOx than ten VW’s and is illegal in all 50 states and Europe. Every 200k miles, clean the manifold and forget about it. Gasoline can be used (with care) to wash that stuff out.
Little known or noticed: your engine has a PCV valve. In another example of brilliant German engineering, it’s built right into the valve cover and is non-replaceable. I’m pretty sure this accounts for more than it’s fair share of manifold sooting. Search for my thread on “valve cover, dissected” to see how this gem works. I’m still looking for a way to repair it.
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When the car was new, yes, the NOx was reduced by the EGR valve. After 30+ years and likely being gunked closed anyway, I doubt there's much of a difference in its performance. The CO and carbon emissions from the tailpipe of a car with an extremely clogged intake manifold are FAR WORSE for the environment than a higher NOx production.
The PCV valve may or may not be contributing to the oil buildup in the intake. My PCV valve is known not to work (even rattles) and I did an experiment with an oil catch can with some paper towel in the bottom. Drove the car for nearly a month and came back to check it. One single solitary drop of oil.
Since I do have a fairly large amount of oil in the intake, there's only 1 other place it can come from - turbocharger. On a higher mileage engine, I'd blame the turbo for oil in the manifold over the PCV system. It doesn't take much of a leak for it to aerosolize the oil and coat the entire intake with it. With a still functional PCV system the oil and soot team up to make a sort of glue that's truly awful to remove.