On this Jeep CCV system, no vacuum is present.

This is a common maintenance issue with 4.0 Cherokees with high mileage from this generation. The CCV (crankcase ventilation) system has gotten clogged with oil sludge, thereby causing crankcase gases to instead flow through the breather tube up front that is only supposed to draw fresh air from the air filter. When the CCV gets clogged, the gases force their way through the breather tube up front and carry oil into the air filter.

To correct this situation, it is simply a matter of cleaning the CCV orifice at the back of the valve cover and also the plastic tube that runs from it to the throttle body. The CCV orifice has no check valve; it's just a simple pass-through fitting. Carefully remove the tube from the top of the CCV orifice, but don't remove the orifice itself or the grommet, as they are probably brittle from engine heat. Get an unbent paper clip and push one end through the orifice to cut through any gunk build-up, then follow up by spraying some carburetor cleaner using the little spray tube.

Next, put the carb cleaner spray tube into the open end of the CCV tubing you already loosened and spray into it until any blockage is cleaned up. You may want to remove the tubing from where it goes into the throttle body to do this if it is really plugged up. Once it is cleared, you can reinstall the tubing and this should fix the problem. Check this every 6 to 12 months to make sure it doesn't get plugged up again.