Oil in air intake, and engine stalls

Question

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?

Answer 1

I know my wife's 1991 Cherokee with the same engine has a PCV, but IIRC I had to get an OEM one from the local Chrysler emporium because my local parts store couldn't supply me with an aftermarket one. The engine is the same so I'd be extremely surprised if your Jeep doesnÜt have a PCV.

If it ended up with a fair amount of oil in the in intake tract there is a chance that the idle control valve needs a clean. If the Jeep runs OK with minimal throttle applied the symptoms would be consistent with the idle control not working properly. A decent workshop manual would normally cover the cleaning procedure for this valve - it's usually not very involved but it helps if you have some instructions.

With proper care these engines are very durable.

Answer 2

It could simply be a clogged rear breather line. In the pcv system it's the one that draws vapor into the intake manifold, and if clogged the vapors will go through the airbox breather instead.

Check the tubes and make sure they flow properly, and if any installed check valves are working. Replacing most of the rear hard breather line with fuel line on both my 89 xj and 90 xj solved the oily filter issue for me.