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My 2014 E350 has recently thrown a check engine light. I plugged in my scanner and got a P2279 which is a “Intake Air System Leak”. I looked around the engine bay and noticed the oil cap had a hairline crack on it. Could this be the potential cause of the vacuum leak?
The cap, even if removed, will not cause that. I don't believe the car has any way of telling if the cap is on or off, unlike the gas cap which it knows right away.
I'm not an expert on all the little things that can cause that code to trip, but I'd suspect it's noticing the intake MAP is higher than normal at idle. If you get a scanner, like Torque Pro, you can see the MAP and compare to others with normal MAP which I'd assume is ~4? Maybe 5, but if it's say 8 then you have an issue. To use Torque (free) or Torque Pro ($5?), you just need that phone app and a cheapo $10 OBD dongle. I got a little blue one from Amazon and it works as well as much more expensive ones:
I have like five different ones from $10 to $50 and this cheapo is my go-to.
I don't believe a small leak can trigger the code, like a small vac line, but if the PCV valve took a dump I imagine it would cause that. As a test you can remove the oil cap while it's fully warm and running. If no smoke comes out then I suppose it's possible the PCV is at full flow, which is too much for idle and lowers your MAP. If smoke comes out or kinda lingers, suggesting very little PVC action, then I'd assume it's fine and not the issue. There is also a tube where the PVC intakes fresh air into the eng and if you put your finger over it and it starts to pull vacuum on your finger, then I'd again suspect the PCV valve. I believe that hose is connected to the intake inches in front of the throttle body.
The old school way to find intake leaks is spray around with carb cleaner and listen for when the eng responds. It needs to be flammable carb cleaner, which I'd assume all are but these days you never know. But when you hit the spot, the rpm should jump a bit, or possibly drop, but it should do something which tells you that carb cleaner was sucked in, therefore a leak.
I know this is just short of impossible with your intake but carb cleaner is cheap and you might get lucky.
Side note; I was wondering if my PCV was blown so I put a gauge on the oil cap. I bought a used cap on ebay, drilled/tapped, and it read 0 at all times. I have a turbo so I wondered if it was seeing pressure. With zero gauge movement I had to check the gauge, but it's good. I also have zero oil in the aforementioned breather tube before the throttle which tells me no air in the eng is going backwards out that tube. It's not uncommon to see some oil in that tube, but being dry as a bone it tells me the PCV is working perfectly.
Another redneck test is, while idling and fully warmed up, rev it to say 2500 for a maybe 10sec so the brakes have good vacuum. Then let it idle and cycle the brakes over and over, fully depress/release, repeat. If you notice after a few to maybe ten or so cycles that the brakes get a little harder to press, it most likely means the low intake vac is real. I believe your car uses the same line for both the PCV and brakes? If so, and the PCV is bad, then it no doubt makes the brake vacuum even worse.
These are all redneck checks for sure, but they are an effective tool. You may, however, need some experience to determine normal from not normal but it's better than nothing Let us know what you find and I'll subscribe to keep tabs if you have redneck questions
E300 w212 | E46 BMW | Golf MK5 | Toyota Tercel | Dodge Intrepid | CBR600
A smoke test would be really helpful finding if there is a leak somewhere.
If no leaks I would start considering replacing the oil cap, PCV, and MAF if you want to go the parts cannon method.
A smoke test would be really helpful finding if there is a leak somewhere.
If no leaks I would start considering replacing the oil cap, PCV, and MAF if you want to go the parts cannon method.
02-18-2023, 09:20 PM
Let us know what you find and I'll subscribe to keep tabs if you have redneck questions 
