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While looking for vacuum leaks to explain a P0171 code, I noticed a sloshing noise/feel when I removed the intake silencer baffle (which is part of the intake tubing that sits between the MAF sensor, and the intake throttle body.)

When I poured this liquid out through one of the baffle's vacuum ports, it was clear like water, but had an oily feel. (Later I noticed it killed my grass.)

What is this, and what causes it to collect? So far my guess is that it is oil fractions from condensed PCV gases. But it is mostly clear, and not brown like the oil residue I usually see build up at the mouth of the throttle body.

How concerning is this?

Cognitive Hazard
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2 Answers2

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I may have just realized the answer to my own question: It was likely SeaFoam that didn't make it past the throttle body. I forgot that I did a SeaFoam treatment a few months ago. The point at which I injected the SeaFoam was downstream from this baffle, and the engine was running at the time (and I had the throttle valve propped open slightly) so it's still a mystery how it got back upstream. However, the color & feel was consistent with SeaFoam.

Cognitive Hazard
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Most engines have the negative side of the pcv system connected to the intake to get fresh air pulled into the engine but when engines have enough blow by that overcomes the pcv system it will blow back into the intake. Blow by contains engine oil. A sign of higher mileage engines.

Another cause of intake deposits is valve overlap where small amounts of exhaust gases are burped into the intake runners with each combustion cycle, but these are usually dry deposits and look like carbon, but if you do a lot of very short run driving these can become moisture infused from condensation.

Moab
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