* PCV System Failure: The PCV system is designed to remove crankcase pressure and blow-by gases (unburnt fuel and oil vapor). If the system is clogged or malfunctioning, pressure builds up in the crankcase. This pressure can force oil past seals (like valve cover gaskets or even piston rings if it's severe) and into the intake system, including the air cleaner. The sputtering and near-stall are likely due to the oily air-fuel mixture disrupting combustion.
* Possible Culprits within the PCV System:
* Clogged PCV valve: This is the most common culprit. The valve regulates crankcase pressure, and if it's stuck closed or restricted, pressure builds.
* Clogged or damaged hoses: The hoses connecting the PCV valve to the intake manifold and crankcase can become brittle, cracked, or blocked with debris, preventing proper ventilation.
* Vacuum leaks: A leak in the vacuum system can also disrupt the proper operation of the PCV system, leading to increased crankcase pressure.
* Worn valve cover gasket: A leaky valve cover gasket allows oil to escape and enter the crankcase ventilation system.
* Other Less Likely Possibilities (but still worth considering):
* Failing piston rings: While less likely to cause oil in the air cleaner *immediately*, severely worn piston rings can lead to excessive blow-by, eventually resulting in oil in the intake. This would likely be accompanied by other symptoms like excessive blue smoke from the exhaust.
* Oil pump issues: A faulty oil pump could lead to excessive pressure, but this is less likely to directly cause oil in the air cleaner box. It'd be more likely to cause low oil pressure warnings.
What to do:
1. Check the PCV valve: This is the easiest and cheapest check. Locate the PCV valve (usually a small, usually plastic valve on the valve cover) and try to gently move the valve. If it's stiff or doesn't move freely, replace it.
2. Inspect all hoses associated with the PCV system: Look for cracks, kinks, or blockages in the hoses connected to the PCV valve and the intake manifold. Replace any damaged hoses.
3. Check for vacuum leaks: This requires more experience, but look for any loose or disconnected vacuum lines. A mechanic can help with this if needed.
4. Inspect the valve cover gasket: Check for oil leaks around the valve cover gasket. A leaky gasket would allow oil to enter the system.
5. If the problem persists after checking the above: A mechanic might need to perform a more thorough compression test or other diagnostic tests to rule out more serious engine issues like worn piston rings.
Start with the simplest and cheapest solutions first (PCV valve and hoses) before moving to more complex and potentially expensive repairs. Ignoring the problem could lead to serious engine damage.
