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Unread 09-21-2013, 07:35 AM   #1
BH97TJ
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1977 CJ7 
 
Join Date: May 2007
Location: Oley, Pennsylvania
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Wj WJ High Idle Issue

I just finished replacing the engine/transmission in my 2000 Laredo yesterday. My issue is that, when I start the Jeep, it jumps to about 4,000 rpm and then shortly after drops to about 3,500 rpm. This is where it is currently idling. Obviously, this isn't correct by a long shot. I double checked all of my electrical connections, grounds, vacuum lines, etc. and nothing changed. Then I called my mechanic and he said to check all of the intake/exhaust manifold bolts again and to make sure that the intake was sitting fully against the cylinder head because of locating the manifold onto the dowel pins on the head. I just finished removing and reinstalling the intake manifold this morning, making sure I torqued all manifold bolts correctly. When I start the Jeep now, I get the same idle as before. What could cause this? Any ideas?

I installed a new intake/exhaust manifold gasket so I don't think that's the issue.

Some items I can think of:
-I painted the block silver (so I can spot any leaks down the road). If I got some overspray in the intake ports, would this cause the high idle?
-I had my battery removed when removing/installing the engine. Does my computer need to be reset or "find itself"? Or, should I reset the computer again since I removed the manifold again?

PLEASE HELP! This is my daily driver and I have to get this fixed up today!!

Thanks in advance!

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Unread 09-21-2013, 07:39 AM   #2
JTS97Z28
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Paint overspray should not cause any sort of extremely high idle like that. As for computer learning, I have never seen an instance where a car started and jumped to 4,000rpm after a battery or computer change. Did anything change at all with your TPS or IAC sensors on the throttle body?
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Unread 09-21-2013, 07:48 AM   #3
BH97TJ
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What do you mean "change"?

I'm using the engine itself from the new (used) engine I got, but all of the accessories (intake, exhaust, a/c comp, etc. are all from my old engine.
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Unread 09-21-2013, 07:50 AM   #4
MattJeep
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My guess would be a bad TPS or massive vacuum leak. Sure your intake gasket is set correctly?
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Unread 09-21-2013, 07:50 AM   #5
narnwv
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Sounds like the IAC is stuck

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Unread 09-21-2013, 08:10 AM   #6
BH97TJ
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I'll check the IAC. I have another from the other engine if the new one is bad. I'm sure the gasket is set right. I've had it off twice now
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Unread 09-21-2013, 09:29 AM   #7
BH97TJ
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Well, back to square one. I swapped, cleaned, and tested every combination of IAC, TPS, and Throttle bodies that I have. It still starts and idles at a high RPM, possibly higher than before.

When spraying some carb cleaner around the manifold/head mating area, I didn't get any changes in RPM.

Any other thoughts?

I appreciate the help
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Unread 09-21-2013, 10:08 AM   #8
Knightrider9827
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Dumb question for ya......is the throttle cable routed correctly? Could it be holding the throttle open?
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Unread 09-21-2013, 10:59 AM   #9
MattJeep
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That was my next guess. But I wasnt 100% sure how the throttle cable is setup.
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Unread 09-21-2013, 01:34 PM   #10
BH97TJ
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Throttle cable comes through the firewall above the intake manifold, goes over to the valve cover and loops back over the valve cover to the throttle body. I did check the routing and cable sticking, but the second time i tried, i didn't have any of the cables connected
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Unread 09-21-2013, 02:19 PM   #11
Knightrider9827
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Is the throttle plate closing all the way? Maybe there's something sticking it open?
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Unread 09-21-2013, 04:14 PM   #12
BH97TJ
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Nope, its fully closed. If i bump the throttle, the RPMs will jump up, but come back and idle at about 4,000
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Unread 09-21-2013, 06:10 PM   #13
86cj74.2L
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What if you let it warm up and see what happens with the idle?

It should not cold idle that high...........

With rpm that high I doubt any type of spray will have a noticeable effect.
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Unread 09-21-2013, 07:26 PM   #14
Knightrider9827
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Try unplugging IAC and starting it up? Do you have a scan tool you can see throttle position on ?
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Unread 09-21-2013, 07:38 PM   #15
MoparMech
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Get a propane tank with about a 6 foot long hose, turn on the propane, and feed that propane all over the engine. Across every vacuum line, every gasket. across the entire intake(checking for possible cracks), brake booster, check the hvac for mode and blend door actuators that are leaking, If the engine changes at all while it is running you have found your leak. Another option is to block off the throttle body with a rubber glove or something that will seal it completely and light up your favorite cigar(unless you have a smoke machine or party fogger) pull off a vacuum line and blow smoke into the intake, search for leaks. Hope this helps.
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