Mystery problem involving air

[98XJblack]

So I have my girls 1998 cherokee limited which she no longer drives and wants to get rid of cause she's sick of the break downs. I've been driving it here and there and couldn't get the thing to die like it does for her, until today. Drove it about a mile until she wouldn't accelerate anymore with hitting the gas. Extremely rough idle, any mention of gas or pulling the throttle would kill the engine. The air intake was very loud like it was just gasping for air or pulling it to nowhere. Out of some weird thought I pulled the oil breather hose from the rear of the valve cover to the intake manifold, engine revved up hard I put the hose back on the intake manifold and idle was smooth and drove the last 40 miles home. No issues.

So I figured out how to cure the problem at the time of issue but what is the underlying cause? Thanks for the help


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[Brasscatz]

Wow, that is an interesting one.... I'll be honest and say that I don't know. Have you cleaned the IAC or anything?

[98XJblack]

I have done nothing besides pulling that tube because I've never had the privilege of experiencing the problem and being able to work it out. I could look at the IAC


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[XJ Wheeler]

Since you said it sounded short of airflow i would check out the airbox and tube to make sure something didn't get sucked in there, or a careless mechanic left something behind. Also, check the area where the airbox gets its incoming air supply for obstructions. Next, clean the iac and throttle body and make sure the butterfly is clear of obstructions. And probably should check out the throttle position sensor for proper function. And as well, a clogged exhaust can keep an engine from revving. Slipping a fuel pressure gauge on might not be a bad idea either, in case its not an airflow issue.

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[slvmart]

I was wondering what the 2 things may have in common. Assuming that this is air supply problem, not the "All out of Love" group (someone quick! Help me get that out of my head !), then how can the vacuum line possibly introduce air into the throttle body ? Since vacuum leaks typically only causes engines to run worse, not better.
This leads me to ask :
Where in the air intake system is there a vacuum line ? If I recall correctly the only vacuum line runs to the filter housing. So can this somehow be restricting air flow ?

[98XJblack]

This is the line I pulled, it's the breather from the rear of the valve cover to the intake manifold behind the throttle body. I'll inspect everything tomorrow for clogs and such, should be in the 50's and nice out.http://tapatalk.imageshack.com/v2/14/11/22/190cf8fecdd9bd9f0117933aff29fecf.jpg


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[dagod16]

I would like to know so please keep us posted.

[ice_cold]

Since its a crank case vent, maybe it and the front one is plugged. If the crank case cannot vent it will hamper performance by pressurizing the engine, something they are not fans of, learned this the hard way..lol
"On your 2000 it is referred to as a Crankcase Ventilation System. It works like a PCV system but uses a metered orifice instead of a PCV valve. That orifice meters the amount of vapors drawn out of your crankcase. The manifold vacuum helps to draw it out through the air box and burn the nasties during combustion."

Hope it helps..

[JeepFreak]

Easy fix to see if it is indeed the CCV (I also have a CCV on my 49 state 1994 XJ). This comes direct from Haynes:

With the engine RUNNING, remove the hose to the CCV and determine if there is a small vacuum on the hose and the hole by placing your finger over it. If there is no suction, the hoses may be plugged or the orifice is. Clean them. If there is suction, your CCV is operating correctly.

In class (auto class in college), we are taught the Occam's Razor theory where the most simple explanation is usually the correct one...and it is....a lot. Start with simple and branch out from there. Check your fuel filter, airbox and filter, IAC and MAP sensor. If the MAP goes, so will your pressure causing a choking of exhaust fumes in the system. If you have an EGR, check there as well. It could be stuck.

[XJ Wheeler]

How's this going for ya?

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[nickyg]

I had to replace mine a while back. here's a short write up I did on it.http://www.xjtalk.com/showthread.php?t=17115

[98XJblack]

I haven't noticed any kind of obstructions upon inspection but haven't replaced or removed the valve cover to inspect the PCV valve elbow. But I may try and replace the elbows and maybe that will resolve the issue. Been dealing with my arthritis recently so I haven't done much work on the car after the work day.


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[98XJblack]

Bought and installed new pcm valve elbow with no end to the phantom bad idle at random times. My gf has decided to call it quits. But just had a random thought and I didn't keep the original valve cover from the new engine because it had writing all over it but I still have it. Anyways the previous was quite filthy inside and out.

Basically what I'm thinking is there might be an area of the valve cover for carbon or junk to build up that I'm not aware of. Pieces could randomly break off and clog the system at their own leisure?


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[4.3LXJ]

Those elbows clog easily. It doesn't take chunks, they just do over a long period of time