Hey fellas, Ive noticed a bit of a rough idle so I'm working my way through finding the culprit. I found a pinhole in the big hose right near the air filter. Could this cause a rough warm idle? There was also about a tablespoon of engine oil in there. Is that normal?
'94 4.0 V6

 

Replace PCV Valve, drivers side valve cover.

There is a hose from oil filler tube to the Air tube, between MAF sensor and intake
That is the vent hose part of the PCV(positive crankcase ventilation) system.

The PCV Valve is there to pull crankcase "blow-by" out of the crankcase and valve covers and burn it in the engine.

When ever a cylinder fires, some of those explosive gases will "blow-by" the pistons rings.
The piston's rings and the cylinder walls are coated in oil, these hot gases vaporized some of that oil.
So crank case is full of that oil vapor when engine is running, and because of the oil drain holes in the head the valve cover areas are also full of that oil vapor.

There is little Blow-by at idle, and high vacuum, so PCV valve works a little different, there is a weighted valve inside, if you shake a PCV Valve you can hear it rattle, no that doesn't mean it is good, lol.
At idle the high vacuum in intake suck the valve up so it is almost closed all the way.
At higher RPMs, more blow-by, less vacuum, the PCV Valve opens all the way and sucks out the oil vapor.
The Vent hose is there to PULL IN fresh air during this time, and is there to at least suck in some of that oil vapor if PCV Valve should fail.

So check that vent hose to see if it has lots of oil inside, clean it out if it does.
Replace PCV valve and clean its hose as well.

You could also have excessive Blow-by, high mile engines can get worn rings so even more blow-by, more than PCV Valve can handle.

After PCV system has been clean and new valve installed, pull out dip stick
Start engine
get a Kleenex or toilet paper and put it over dipstick hole, it should not blow off should be held down a bit, not much, but if you have lots of air flowing out of dipstick tube you have excessive blow-by

 

Thanks Ron. Are you suggesting I replace the valve cover? Or are you just telling me the PCV valve is located there? Do you think I can get away with cleaning the valve? I guess it's not really worth the hassle for such a cheap and easy part to replace?

 

Yes, replace PCV Valve and make sure its grommet(rubber ring it slides into) in the valve cover is OK.
Valve covers do not need to come off or be replaced.