Jeep maintains high RPM's. Need advice

[Babygools99]

I have a 1999 with a 4.0, ax-15 5 speed. My Jeep generally wont idle high once its first started, but after i get moving and come to a stop, the RPM's won't come back down to idle unless i give the gas pedal a quick rev.
It's done this for a while, it's just aggravating me now and i want it to be fixed. Any advice?

 

[Daryl]

I have a 1999 with a 4.0, ax-15 5 speed. My Jeep generally wont idle high once its first started, but after i get moving and come to a stop, the RPM's won't come back down to idle unless i give the gas pedal a quick rev.
It's done this for a while, it's just aggravating me now and i want it to be fixed. Any advice?

Spray some carb cleaner around the intake where it bolts to the head and see if the engine rpm increases. Also inspect all the vacuum lines.

 

[Indy]

Start with basics. Clean the throttle body, IAC (Idle Air Control) valve and make sure the throttle cable is not sticking.

 

[ranger101]

https://wranglertjforum.com/threads/how-to-clean-your-iac-idle-air-controller-valve.662/

 

[bromel]

I had the same problem. Cleaning the IAC fixed it.

 

[D M]

I had this problem in johnson valley, disconnect your battery, clean the IAC, plug in the battery and start the car. Also while the car is running, remove the intake elbow and box and spray about 1/3rd of a can of b-12 chemtool(carb cleaner) into the throttle body to where it almost dies, let it come back, repeat

 

[ranger101]

I had this problem in johnson valley, disconnect your battery, clean the IAC, plug in the battery and start the car. Also while the car is running, remove the intake elbow and box and spray about 1/3rd of a can of b-12 chemtool(carb cleaner) into the throttle body to where it almost dies, let it come back, repeat

I’ve never used this method(have seen it mentioned a few times) but I can say that simply removing it and spraying it out, doesn’t always fix it. Though it did slightly improve things. I’ve done that twice with mine but will be trying this method next.

 

[D M]

I’ve never used this method(have seen it mentioned a few times) but I can say that simply removing it and spraying it out, doesn’t always fix it. Though it did slightly improve things. I’ve done that twice with mine but will be trying this method next.

I would suggest a vacuum leak then, check around your brake booster and charcoal canisters, those are very common spots for vacuum leaks. Also if you can, do a smoke test.

 

[Babygools99]

I would suggest a vacuum leak then, check around your brake booster and charcoal canisters, those are very common spots for vacuum leaks. Also if you can, do a smoke test.

My pcv(or ccv, whatever the name is) on top of the valve cover has hardened up and oil is coming out the top. The elbows don't look dryrotted. Would this cause a vacumn leak?

 

[bromel]

My pcv(or ccv, whatever the name is) on top of the valve cover has hardened up and oil is coming out the top. The elbows don't look dryrotted. Would this cause a vacumn leak?

Not a significant one.

 

[Jerry Bransford]

I had this problem in johnson valley, disconnect your battery, clean the IAC, plug in the battery and start the car. Also while the car is running, remove the intake elbow and box and spray about 1/3rd of a can of b-12 chemtool(carb cleaner) into the throttle body to where it almost dies, let it come back, repeat

Just remember the engine has to be at idle rpms in order for the spray to pass through the IAC and its orifice in the throttle body. Raising the rpms off idle will cause the cleaner to bypass the IAC and just clean the inside of the throttle body leaving the IAC uncleaned.

But for higher than normal RPMs I'd be looking more for vacuum leak than a dirty IAC which normally cause lower-than normal idle rpms.

 

[D M]

My pcv(or ccv, whatever the name is) on top of the valve cover has hardened up and oil is coming out the top. The elbows don't look dryrotted. Would this cause a vacumn leak?

Don't take my word for it, but I don't think so. It wouldn't hurt to replace that anyway, but as others said look around for cracked lines

 

[Jerry Bransford]

My pcv(or ccv, whatever the name is) on top of the valve cover has hardened up and oil is coming out the top. The elbows don't look dryrotted. Would this cause a vacumn leak?

No.

 

[Zorba]

My pcv(or ccv, whatever the name is) on top of the valve cover has hardened up and oil is coming out the top. The elbows don't look dryrotted. Would this cause a vacuum leak?

As you describe it here, no. However, it *is* possible to get a vacuum leak from this area if the rear elbow has a crack in it or is the wrong one. Easy enough to find out - disconnect the hose from the elbow and plug it (the hose). If the RPM problem goes away, there's you go. If not, not. Of course, there could be a vacuum leak at the other end of that particular hose where it connects to the intake manifold - inspect its entire length. The IAC and throttle body should be cleaned regardless while you're working on this - mine was filthy. I suggest a new throttle body gasket while you're at it.

This probably doesn't apply since you've owned the Jeep for awhile, but DO make sure that the ccv elbow (rear elbow) is the one with the restricter - about a 60 mil (.060") diameter insert - NOT the "full diameter" as the front one is. I learned that this one the hard way, my Jeep came to me with a newly installed incorrect rear elbow that equated to a "vacuum leak deluxe" with high idle all over the place. Many auto parts places do not list nor carry the correct rear elbow, they only seem to have the front style but may list it for both. I found that out the hard way as well - had to order the correct on online! As soon as it went in, all problems went away!

 

[Babygools99]

As you describe it here, no. However, it *is* possible to get a vacuum leak from this area if the rear elbow has a crack in it or is the wrong one. Easy enough to find out - disconnect the hose from the elbow and plug it (the hose). If the RPM problem goes away, there's you go. If not, not. Of course, there could be a vacuum leak at the other end of that particular hose where it connects to the intake manifold - inspect its entire length. The IAC and throttle body should be cleaned regardless while you're working on this - mine was filthy. I suggest a new throttle body gasket while you're at it.

This probably doesn't apply since you've owned the Jeep for awhile, but DO make sure that the ccv elbow (rear elbow) is the one with the restricter - about a 60 mil (.060") diameter insert - NOT the "full diameter" as the front one is. I learned that this one the hard way, my Jeep came to me with a newly installed incorrect rear elbow that equated to a "vacuum leak deluxe" with high idle all over the place. Many auto parts places do not list nor carry the correct rear elbow, they only seem to have the front style but may list it for both. I found that out the hard way as well - had to order the correct on online! As soon as it went in, all problems went away!

Thanks for the info on that! The jeep just turned over 231k, and i've cleaned the iac about 50k miles ago. But i dont think i did it properly, so i'm going to give it another go. Do you happen to remember where yiu got your correct parts for the ccv? I figured i would change it as well while im digging around looking for any potential vacumn leaks.