I have 1999 C230 with a CEL and P0170 code, which points me to the Air Mass Meter sensor. So I removed the AMM to clean it with CRC MAF cleaner. It was soaked with oil. The pipe coming from the air cleaner also has oil all over, and one of the large hoses coming into the air cleaner box is coated with a black tarry film.

I sprayed the sensor down with the cleaner, and now the engine runs better (for now), but where could the oil be coming from?

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2008 ML350
2007 Honda Element
2007 Honda Accord
2009 Honda Civic