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Topic Review (Newest First)
10-13-2009 12:08 PM
Jnixon Thanks a lot for the help. I will take a look at that.
10-13-2009 10:38 AM
nagymjr As for my Jeep the problem has been solved. I sold

Seriously, we did fix it before selling the Jeep. I replaced the broken elbow on the front of the valve cover, replaced the CCV hose from the valve cover to the intake, and removed/cleaned the valve cover. This did help make the engine run smoother at idle and while driving, but the high/intermittent idle did come back.

The culprit ended up being the fuel pressure regulator/filter. I replaced the whole assembly (expensive), but it did the trick. I had a mechanic friend check the pressur at the rail with his gauges. We could see it running at normal PSI then drop a bit and then a sudden surge like it was compensating to bring the level back to normal. After weeks with the new regulator the problem never came back.

Then i sold her and kept my Blue 02 4banger because it needed nothing and the wife put the lock down on money to fix the project Jeep.

Hope this helps.
10-13-2009 10:15 AM
High Idle 98 Sahara

Did you figure your problem out?
My Sahara is doing the exact same thing.
I have new IAC
New distributor
Checked TPS with V meter
I did notice that when I pulled the CCV out of the valve cover and covered the vaccum hose the idle came down. Should there be vaccum at idle there?
08-13-2009 04:52 PM
mrcarcrazy highly doubt its clogged. Usually there's just a baffle in the valve cover to keep oil from being splashed up into the PCV setup...not much to clog really. no combustion takes place anywhere near there, so carbon shouldn't be there. Burnt oil very possibly, but it shouldn't clog up. not to mention many people slap a small vent filter to the PCV location, and cap the other end (on intake tube)

High idle is usually due to vacuum leak.
08-13-2009 04:35 PM
nagymjr OK, I installed the factory replacement and things were ok for about 10 minutes idling in park them BAM it started again.

When I removed the broken elbow and grommet i noticed that the internal valve cover side of the elbow/grommet was pretty dirty with carbon deposits and soot. Now I believe this is at the front of the air flow through the PCV/CCV system. My thinking is if this is at the front and is very dirty with deposits then the actual CCV output of the valve cover is probably really bad and/or partially clogged. This would cause the same symptoms right?

Is my line of thinking correct?
08-12-2009 08:03 PM
rrich PCV systems have been around for a long time. The military invented them - or someone in the military. Engines were sludging up bad travelling at walking speed - WWII. Till then they used road draft tubes to suck out the fumes. But going so slow the road draft tubes did nothing.
Someone hooked the crankcase to vacuum through a small hole. Later on they put a valve in that line to help prevent the crankcase from igniting in case of a backfire.
It evolved from there.

Do a search on Yahoo - PCV systems - plenty of info and the history.

Jeep uses a very simple one, but none are complicated.

In the mid 60's many cars didn't have them - yet. They had to be retrofiited. I must have installed close to 1000! I was paid $2 or $3 apiece for them. They got a bad rap because so many installers did it wrong.

Most Kids in parts houses today don't have a clue - in their previous job they chopped onions for hamburgers. But what can you expect for just $35/hour?
08-12-2009 03:17 PM
djwilbanks I know, I was just making sure I was being clear... cuz I rarely am.
08-12-2009 03:04 PM
nagymjr rrich,

that was somewhat my feeling. I can't believe how there isn't much out there on this topic especially for the popular 4.0L. I was shocked that none of the auto part stores carried these parts. I found two older Cherokee write-ups that touched on cleaning the valve cover and internal flapper/pcv type valve and another about replacing the hose to the intake manifold. That was it. no logical explanation on how the PCV/CCV system works or flow diagrams.


I wasn't calling you out, just trying to clarify for my own knowledge. I appreciate the input.
08-12-2009 02:58 PM
rrich The parts guy either slurred his words or didn't use the right words.

PCV - Positive Crankcase Ventilation - there are several variations. It's purpose is to remove the fumes that build up in the crankcase - they get sucked into the intake where they get sucked into the cylinders and safely burn. The elbow end lets clean fresh air in. No loss the performance.

If they just vented to the atmosphere we'd have to breathe them. Yuk!
08-12-2009 02:45 PM
djwilbanks The "CCV" is probably Crankcase Ventilation. Every manufacturer has a different name for it, but it all does the same thing. It may not be a true PCV system, but it works the same...

As I said, I have been mistaken before, I may have my PCV system reversed in my head, either way, a leak that size can cause unmetered air to pass and can upset the A/F ratio.

As long as you have the correct part on order, you'll know pretty quickly if it helped your situation.
08-12-2009 02:40 PM
rrich At the other end of the valve cover is the PCV Valve - sort of. It's a small fixed orifice in the end of the plastic tube sticking in the grommet. The tube is connected to manifold vacuum. It sucks fumes from the crankcase with vacuum.
The front end - including your elbow - lets air in the front of the engine - clean air from the air filter tube. That clean air "sweeps" the fumes out of the engine to the PCV.

It's just an elbow, but a standard elbow may not work - you may need to get it from the dealer - shouldn't be expensive.

Yes, it's an uncalibrated source of air - could very well be your idle trouble. The IAC can only do so much in controlling idle speed, that big a leak is beyond it's capability.

Suggestion - after the new elbow is in, disconnect the battery overnight, or at least for several hours. What that does is resets the computer's memory back to default - the previous problem is forgotten.
Everything should return to normal.

Yes, for several hours - short term or even with a scanner does not clear the memory the same - codes dissapear, but it still will try to compensate for a problem that no longer exists.
08-12-2009 02:00 PM
Originally Posted by djwilbanks View Post
Uh.. That should be part of the PCV (positive crankcase ventilation) system. If that elbow was broken it could, I believe, cause a high idle rpm. But, unless I'm mistaken the elbow
should channel unspent gasses from the engine into the intake for recycling. It's mostly an emissions control, but it can cause poor performance when the system is disrupted.

I'd replace the elbow, and if that doesn't work the PCV valve may be stuck which can cause idle speed issues. Might need to be replaced.

When i ordered the part the guy said it was part of the "CCV" system. I'm not sure about cycling the unspent gases though. It was sucking air into the valve cover from the cold air filter tube.

Also, from what I have read the 97's 4.0L has a CCV hose (rear elbow on valve cover) because there is a flapper built inside the valve cover that takes the place of a true "PCV". Correct me if I am wrong guys.

Anyways, I will have the elbow tomorrow and give it a try.
08-12-2009 01:25 PM
djwilbanks And it can cause poor fuel economy when the system doesn't work, as well.
08-12-2009 01:24 PM
djwilbanks Uh.. That should be part of the PCV (positive crankcase ventilation) system. If that elbow was broken it could, I believe, cause a high idle rpm. But, unless I'm mistaken the elbow
should channel unspent gasses from the engine into the intake for recycling. It's mostly an emissions control, but it can cause poor performance when the system is disrupted.

I'd replace the elbow, and if that doesn't work the PCV valve may be stuck which can cause idle speed issues. Might need to be replaced.
08-12-2009 01:11 PM
nagymjr Below are the pics. I ordered a new elbow from the local dealer. I removed the hose from the air intake tube and put my thumb over it. It sucked my thumb in so there was definitely some vacuum pressure. It jumped up in RPM's right after. I tried to seat it as best as I could and hold it there, but I'm not sure if I got a good connection. There was definitely some reaction. I just couldn't tell if I was inducing it.
Attachment 10437
Attachment 10438
08-12-2009 11:50 AM
Jerry Bransford Can you post a pic of the fresh air inlet? What happens to the idle rpms if you cover that inlet with your thumb etc. ? If thats a vacuum line, a leak there can definitely cause a higher idle.
08-12-2009 08:49 AM
CCV and Fresh Air Inlet

As I am in the process of deciding what to do with the two Jeeps I own (that discussion is in another thread), I am continuing to work on the 97 Sahara with 200k on it.

I am still having some trouble with the idle jumping up to 1400rpm when in park or nuetral. It runs ok when driving, but if I maintain a constant speed/rpm I can notice a little hitch in rpm and power. Example: when maintaining 2000 rpm's when driving i'll get a dip to 1800 then it will go right back to 2000.

Jerry told me to clean the IAC and I did. It was pretty gummed up. The rest of the throttle body was cleaned and is in pretty good condition. The problem seemed to go away for the first half of the test drive but came back when i got home. I put it in park and boom, its back up to 12-1400 and bouncing down to normal occasionally. So, I replaced the IAC solenoid/drive and same results.

I was also told by a mechanic that it should be the IAC (check first), like Jerry said, and then after that it would most likely be a vacuum leak.

I noticed the "FRESH AIR INLET" elbow in the front of the engine is broken. Will this cause a vacuum leak? I had to electrical tape it together for now, but it doesn't stay together well. Also, could the CCV be clogged or affecting this in some way? What is the actual purpose of these two items?

Thanks for the help in advance.

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