I have a 1994 Jeep Grand Cherokee Laredo 4x4, with the 4.0L inline-six engine.
Recently, the car has been demonstrating some trouble maintaining idle. It usually would not stall outright, but the RPMs would drop extremely low whenever I let off the gas. The car idles relatively okay on first start - the problem only seriously presents itself when letting off the gas to come to a stop or make a slow turn.
Today, the problem finally worsened to the point that it will actually stall. In city driving or parking lots, I have to keep my foot on the gas at all times to keep it from stalling in turns or stops.
My step-dad suggested it might be overdue for an air filter change, and that I should test the problem without the filter. When I opened the air box, I found that parts of the filter had oil in it and there was some oil in the intake tube leading to the engine. Testing the problem with the filter off yielded no change. The car idled well enough immediately after starting but, after applying a light, quick burst of the gas pedal, it quickly stalled.
A Google search for oil in the air intake turned up a lot of results relating to the PCV valve. I checked with my local parts shop though, and they say that my car didn't originally come with one.
What else could cause these symptoms?