Run a compression test. If compression is within specs, the problem is a clogged PCV tube.
Modern engines do not vent the crankcase to the atmosphere. They are closed systems. There are two tubes to provide ventilation (and pressure control): the intake tube comes off the air intake somewhere between the air filter and the throttle body (forgive me for not being more specific, but I've never worked on a '94 4-cyl so I don't have specifics), and goes into the front of the valve cover. The suction side probably comes off the rear of the valve cover and goes to the throttle body or intake manifold. It may or may not have a PVC valve in it. The older 4-cyl engines use a real PCV, but the 6-cyl engines (at least the early ones like mine) don't.
If the PCV valve gets clogged, or if it's a small aperature tube like on the 4.0L and that gets clogged, any blowby pressurizes the crankcase. The crankcase fumes are supposed to get sucked into the engine and burned -- if they can't go there, they get out anywhere they can.