2000 TJ High Idle - JeepForum.com
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post #1 of 10 Old 10-13-2019, 08:33 PM Thread Starter
golphnut01
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2000 TJ High Idle

Hello everyone. I am new to the Jeep Forum and I need some help. I just purchased a 2000 TJ that has the 4.0 with a manual transmission. The Jeep has 148,500 miles on it and has not been offroaded at all that I can tell. The previous owner at some point installed an AEM Brute Force cold air intake and it also has a spacer under the throttle body. I bought the jeep knowing it was idling high and now it is time to get it fixed. It was idling up around 1800 rpm’s. We found one vacuum line off and fixed it. That brought the rpm’s down to 800 for a short while and now it is back up to 1500. It threw a code pointing to the IAC. I took the throttle body off to clean it and the IAC. When I started it up I thought it was fixed. 800 rpm’s for a short while then back to 1500. I can slow the vehicle down and drag the rpm’s down to 1000 only to push the clutch in and it jumps up to 1500. I don’t see any vacuum leaks and the IAC has been cleaned. How common is it for that control to just go bad and need replacing? Any suggestions would be greatly appreciated. I also hear a squeal when I accelerate and decelerate. I hear that is common with some of these cold air intakes.

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post #2 of 10 Old 10-13-2019, 08:48 PM
mukluk
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Try to replicate the accel/decel squeal while the Jeep is parked -- what you're hearing may be a vacuum leak causing your high idle. So long as it isn't really dusty or there's a bunch of stuff blowing around in the air, it's fairly safe to temporarily remove the air intake tube from the throttle body and run the engine to rule it out as a source of the noise.

Have you tried spraying sensor safe intake cleaner at all suspect vacuum leak locations?
Are any of the intake manifold or throttle body fasteners loose?
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post #3 of 10 Old 10-13-2019, 08:51 PM
AjRagno
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Sounds like you still have a vacuum leak on the intake side. Next area to check is the vacuum elbow on the MAP sensor. Take it off, squeeze and bend it to see if it's cracked.

I believe that on the 2000 4.0L, there will also be at least one unused vacuum port on the intake manifold that needs to be plugged. Also take a look at all of the vacuum lines coming off the intake manifold and trace them back to the fire wall to make sure they are all connected, not cracked or otherwise leaking.
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post #4 of 10 Old 10-14-2019, 12:44 AM
TheBoogieman
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If there isn't any vacuum leaks, replace the IAC with a quality one.

Quote:
Originally Posted by jeepinmichguy_ View Post
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post #5 of 10 Old 10-14-2019, 06:25 AM
jtec
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Mukluk suggested
"Have you tried spraying sensor safe intake cleaner at all suspect vacuum leak locations?"

This should be easy fast - do yuu understand how to do?

Also posting all code #'s - would be helpful.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 10 Old 10-14-2019, 03:47 PM Thread Starter
golphnut01
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I guess this is the way to reply. I don’t see an individual reply to each one of your responses. I am taking notes from all of your responses and I am grateful for the help.
I have taken the throttle body off and cleaned it.
I removed the IAC and cleaned it.
I have not gone into near the detail examining vacuum lines that y’all are suggesting so I will do that next. I do see one post on this jeep that does not have a line on it and is not capped. That might be the problem. I will check that and see if there is any vacuum there.
What is the best way to look for a vacuum leak? I can inspect with no problem. I assume y’all are looking for the leak to pull the cleaner in when I spray around it. Unfortunately I can’t do any of this till Friday. I work out of town. I will post what I find probably this next Sunday.
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post #7 of 10 Old 10-15-2019, 12:23 AM
TheBoogieman
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Check the ends and T for cracks.
Attached Thumbnails
Vacuum line pic.jpg  
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Quote:
Originally Posted by jeepinmichguy_ View Post
TheBoogieman is a jerk.
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post #8 of 10 Old 10-18-2019, 02:09 PM Thread Starter
golphnut01
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I had a chance to look deeper into vacuum leaks today. There are three vacuum ports on the manifold. The back two have hoses on them but the front has nothing and it is sucking air. From some of the other searches I have made I believe this port is supposed to have a cap on it. Either that or a line is missing all together. Does anyone know if that port is supposed to just be capped?
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post #9 of 10 Old 10-18-2019, 02:24 PM
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Quote:
Originally Posted by golphnut01 View Post
I had a chance to look deeper into vacuum leaks today. There are three vacuum ports on the manifold. The back two have hoses on them but the front has nothing and it is sucking air. From some of the other searches I have made I believe this port is supposed to have a cap on it. Either that or a line is missing all together. Does anyone know if that port is supposed to just be capped?
Have someone plug it OR put your finger on it to plug it, while running, and see what happens to your idle. I can't picture where it is, to tell you whether it is missing a cap or a vacuum line to connect to something. You shouldn't hear ANY vacuum lines hissing...

2006 LJR...the madness begins again
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post #10 of 10 Old 10-18-2019, 03:49 PM
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Quote:
There are three vacuum ports on the manifold. The back two have hoses on them but the front has nothing and it is sucking air.
If you're talking about the ports on the side of the manifold below the throttle body, cap it. One line should run to the EVAP system mounted atop the left inner fender, the other smaller line is shown in the diagram posted earlier. The only other vacuum hoses/lines you should have attached to the manifold are the one running to the brake booster, and the one running to the CCV atop the rear of the valve cover.

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