What causes oil to leak into the mass air flow?

i recently took the intake manifold off of my 2001 vr6 jetta because i needed to replace the injectors, when i took it off i noticed it was very dirty with oil sitting in the mass airflow. i have no idea where the oil comes from. any ideas would be great. thanks.What causes oil to leak into the mass air flow?
If there's none in the air filter container..you need to figure when the oil is accumulating..during the motor's operation..or when turned off.What causes oil to leak into the mass air flow?
There's a line that goes to the valve cover to pull air in from the top of the valves. Sometimes oil can seep past the PCV where that vacuum line pulls air from the valve cover and it will get into the tube and throttle body. If you were changing the injectors, it might be from a PCV going bad and letting a lot of oil get through and mixing with the air and fuel.


As long as it's not pooled up in the intake, it should not be a problem right now. However, the PCV is easy to change and not expensive so you can change it out if you're concerned about it.


Another thing to look at is the throttle body, if there's a LOT of oil on it, then change the PCV and use carb cleaner to remove it the oil from the butterfly.
I'm wondering if you have an aftermarket oil impregnated foam air filter that was over oiled? Your vehicle uses a very sensitive hot film sensor so I would recommed an O.E. air filter only.





You should use an good quality electronic parts cleaner and clean the oil from the intake hose and the Mass Airflow sensor. You may have induced some service codes that require checking.
Normal accumulation of crankcase vapour or blow-by gasses introduced by the positive crankcase ventilation system. You don't have to worry about this until it gets excessive (air filter and housing dripping wet with oil).