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Old October 10th, 2013, 06:59 AM   #1
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Default High idle/rpms

2002 TJ 4.0L
140k Miles
32RH Auto

Hello all, lately my jeep has been acting very funny on me. About a week ago I noticed that after I had driven the jeep (duration didnt matter) and went to park it, as I put it in park, the rpms would shoot up, then slowly go down. It went from doing that all of the time to, now when sitting idle at a light, or just in park, the rpms will gradually rise, then fall, then go back up then down.

What makes this more odd is I noticed that when I go to turn on my heat (for one the heat isn't working properly it is only coming out of the defrost vents) the rpms will go up, and the pressure of the heat when it exits the vents will increase. Then when the rpms drop, so does the heat pressure exiting the vents.

I'm not sure if this is a IAC issue, or TPS issue. I know my throttle plate is clean cause I keep it clean. I'm almost wondering if this has something to do with those vent hoses having a leak? But I'm not sure if that can cause spiratic high rpms or not. Not to mention the heat only coming out of the defrost vents issue occurred the end of last winter. This high rpms didn't occur until a week ago.

Thank you

Ryan
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Old October 10th, 2013, 07:04 AM   #2
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my $.02

Always check for vacuum leaks first. Cheapest to fix and biggest overlook. You might even fix your heat in the process. The vent controls are typically run off of vacuum, I've never owned a TJ so I don't know 100%.

IAC would be my next guess. There should be specs online for testing yours to see if it is good or not. usually with a multi meter. If you don't have one, I would recommend a cheap one from Lowe's (I'm currently using a pocket extech with great results).
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Old October 10th, 2013, 07:12 AM   #3
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sounds like the iac is working fine and you have a vacuum leak in the hvac system. x2 on checking for leaks.
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Old October 10th, 2013, 08:38 AM   #4
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Ah great just what I wanted to hear. I had a feeling it was the vaccume system, but was hoping otherwise.

When the vaccune problem first started last winter, my cruise control went out as well. I knew that it was vaccume related so I took a look at the vaccume hoses and sure enough one of them was cracked and another dangling freely. Unfortunately, I went to the dealer for the vaccume hoses only to find out that they didnt carry them..???

My next option was to go to the junk yard, but when you live 10 miles from Detroit and go to a junkyard for jeep parts, especially a wrangler, you won't find one. And if you do, all that's left is the frame. I pulled some vaccume hoses off of a Cherokee, but their setup is a bit different. Some of the hoses are also wider, and some narrower. I made the best of what I could and pretty much rigged the whole vaccume system.

I ended up getting the cruise control to work, and the heat slightly better, but not 100%. I thought it may be the vaccume system cause I know it wasn't done perfectly right the first time, but I didn't have much of a choice with no exact replacement hoses available.

So where exactly can I get these vaccume hoses, any ideas? Also is there a way to check for the leak? I looked at the hoses and they all look fine, and I can't hear any hissing. I've heard you can spray wd40 in an opening and it will raise the idle, is this true?

Thank you,

Ryan
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Old October 10th, 2013, 08:51 AM   #5
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yes you can spray wd40 into a vacuum leak and it will raise rpm but this is tough to do for hvac vacuum leaks. You will need to just start tracing the hoses back from the TB. You can get a mityvac and pull a vacuum on the system and listen for leaks. Its a lot easier to do this than running the engine. The vacuum lines can just be any standard rubber vacuum line bought at the auto parts store. You can get a few different sizes and use what you need. Nothing really special about the lengths of them.

If you want, you can start at the end and work backwards as well. Sometime this helps to troubleshoot. Start with taking the lines off at the HVAC unit and testing each hose with the mityvac. Check to see if the individual plungers will hold vac. Keep testing back until you get to the firewall and then test the engine side.

this may help.

There really is no easy way to test the whole system. Just start at what doesn't work and move from there.
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Old October 10th, 2013, 09:03 AM   #6
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Quote:
Originally Posted by Catnip 0_o View Post
Ah great just what I wanted to hear. I had a feeling it was the vaccume system, but was hoping otherwise.

When the vaccune problem first started last winter, my cruise control went out as well. I knew that it was vaccume related so I took a look at the vaccume hoses and sure enough one of them was cracked and another dangling freely. Unfortunately, I went to the dealer for the vaccume hoses only to find out that they didnt carry them..???

My next option was to go to the junk yard, but when you live 10 miles from Detroit and go to a junkyard for jeep parts, especially a wrangler, you won't find one. And if you do, all that's left is the frame. I pulled some vaccume hoses off of a Cherokee, but their setup is a bit different. Some of the hoses are also wider, and some narrower. I made the best of what I could and pretty much rigged the whole vaccume system.

I ended up getting the cruise control to work, and the heat slightly better, but not 100%. I thought it may be the vaccume system cause I know it wasn't done perfectly right the first time, but I didn't have much of a choice with no exact replacement hoses available.

So where exactly can I get these vaccume hoses, any ideas? Also is there a way to check for the leak? I looked at the hoses and they all look fine, and I can't hear any hissing. I've heard you can spray wd40 in an opening and it will raise the idle, is this true?

Thank you,

Ryan
Just find out what size lines you need and get universal line from your auto parts store of choice.
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Old October 10th, 2013, 10:05 AM   #7
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Quote:
Originally Posted by Dylan View Post
yes you can spray wd40 into a vacuum leak and it will raise rpm but this is tough to do for hvac vacuum leaks. You will need to just start tracing the hoses back from the TB. You can get a mityvac and pull a vacuum on the system and listen for leaks. Its a lot easier to do this than running the engine. The vacuum lines can just be any standard rubber vacuum line bought at the auto parts store. You can get a few different sizes and use what you need. Nothing really special about the lengths of them.

If you want, you can start at the end and work backwards as well. Sometime this helps to troubleshoot. Start with taking the lines off at the HVAC unit and testing each hose with the mityvac. Check to see if the individual plungers will hold vac. Keep testing back until you get to the firewall and then test the engine side.

this may help.

There really is no easy way to test the whole system. Just start at what doesn't work and move from there.
Alright will do, you've been a ton of help.

I just have 2 more questions

One, I've heard you have to use a specially coate heat treated hose, is that true or will the rubber be fine?

Also there are these plastic orffces that some of the lines plug into. It's like this little plastic adapter thing that lets air through it one way but not another. Are these necessary and if so does it matter which way they let air in and not out?

Thanks once again :)
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Old October 10th, 2013, 10:16 AM   #8
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vacuum lines are rubber hoses. Nothing special about them.

The plastic things are check valves and yes they have to be installed in the correct orientation. Again you can find those at the parts store also. Look for vacuum check valve.
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Old October 10th, 2013, 10:20 AM   #9
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Quote:
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One, I've heard you have to use a specially coate heat treated hose, is that true or will the rubber be fine? Rubber should be fine unless they are resting ont he header

Also there are these plastic orffces that some of the lines plug into. It's like this little plastic adapter thing that lets air through it one way but not another. Are these necessary and if so does it matter which way they let air in and not out?They are most likely there for a reason. check valves should allow air to be sucked through them towards the motor. orifices don't matter which way. blow/suck into them if they are clean and you'll know direction.
Another way to check for vaccuum leaks would be to look for where the vacuum line goes through the firewall to the hvac system. disconnect and plug it and see if your problem goes away. then you'll know if it is a vacuum leak associated with the hvac in the vehicle. if you still have a problem, you at least know it is all in the engine bay, vacuum related or not.
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Old October 10th, 2013, 10:32 AM   #10
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Another way to check for vaccuum leaks would be to look for where the vacuum line goes through the firewall to the hvac system. disconnect and plug it and see if your problem goes away. then you'll know if it is a vacuum leak associated with the hvac in the vehicle. if you still have a problem, you at least know it is all in the engine bay, vacuum related or not.
Or you have multiple leaks and you will spend forever chasing them all and give up and set it on fire
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Old October 10th, 2013, 10:34 AM   #11
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Or you have multiple leaks and you will spend forever chasing them all and give up and set it on fire
before you set it on fire, sell it to me for scrap price so I can have yet another project. I gotta catch up to skooter
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Old October 10th, 2013, 11:29 AM   #12
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Lol I know what you mean, some of these issues can take forever to find and eventually you get to a point where you just don't care anymore. I'm gonna buy 2 different size hoses and see what I can come up with, ill let you guys know what happens
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Old October 10th, 2013, 11:51 AM   #13
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I'm not super familiar with the 4 liters, but an intake manifold gasket leak might also cause havoc with the vacuum system.
Do you hear any lean-popping out the exhaust in the 2300 - 2800 RPM range?
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Old October 10th, 2013, 03:39 PM   #14
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I'm not super familiar with the 4 liters, but an intake manifold gasket leak might also cause havoc with the vacuum system.
Do you hear any lean-popping out the exhaust in the 2300 - 2800 RPM range?
No I can't say that I have, but last time I took it up to those rpms I was on the hwy and we all know how well you can hear on the hwy in a wrangler
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Old October 10th, 2013, 04:08 PM   #15
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We'll their are 2 common vacuum leaks,one is the vacuum resavor under the battery tray. The other common leak is at the intake by the brake booster where the line hooks to the intake, send me your phone and I will send you a picture
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Old October 18th, 2013, 12:52 PM   #16
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I ended up pulling the throttle body apart and replace both the TPS and IAC. Also noticed where the IAC sits was very dirty. Now she's runs great! Thanks for the help guys.
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