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Unread 01-18-2012, 05:22 PM   #1
ROTTEN
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1994 YJ Wrangler 
 
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High idle. Just swapped my 2.5 TB for a 4.0 TB

Just did the swap Monday. Upon startup when cold it rpms at 2100 then drops down after a minute

Will this hurt the engine? It's supposed to be 5 when I leave tonight

We re used the iac and Tps from the 2.5
Ground the tab on the 4.0 tb off
New gasket for the tb

Anyone have this experience? I've driven about 20 miles since the swap
More power but the high rpms bother me

Also it seems my temp is running hotter now

I'm concerned that it will hurt the engine upon start up

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Unread 01-18-2012, 05:32 PM   #2
BackRoadJPin
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Quote:
Originally Posted by ROTTEN View Post
Just did the swap Monday. Upon startup when cold it rpms at 2100 then drops down after a minute

Will this hurt the engine? It's supposed to be 5 when I leave tonight

We re used the iac and Tps from the 2.5
Ground the tab on the 4.0 tb off
New gasket for the tb

Anyone have this experience? I've driven about 20 miles since the swap
More power but the high rpms bother me

Also it seems my temp is running hotter now

I'm concerned that it will hurt the engine upon start up
I had the exact same issue several years ago, if I recall I cleaned things up really well, and I used the same parts as you did to remedy the problem. Make sure everything is sealed nicely and that everything is clean and working proper.
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Unread 01-18-2012, 05:41 PM   #3
ROTTEN
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Yeah it's all sealed up

BUT the 2.5 parts were very dirty
Iac had soot and oil on it and the Tps was the same

When they were on the 2.5 tb I was getting an idle of 1600 at start up and stumbling until the engine warmed up

Should I replace these two items?
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Unread 01-18-2012, 06:16 PM   #4
BackRoadJPin
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I just cleaned them really good, and I reset the computer as well just in case, mine would not idle down for the longest time. In fact when I first swapped it all over the idle ran straight up to redline. Clean everything up, while doing so disconnect the battery to let the computer reset. It was when mine jumped to redline that I realized I had to swap some of the 2.5 parts back over.
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Unread 01-18-2012, 06:29 PM   #5
ROTTEN
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Hmm. I never took the battery cables off. Do you think that is a big step I should do? How long should they stay off?
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Unread 01-18-2012, 07:14 PM   #6
BackRoadJPin
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Quote:
Originally Posted by ROTTEN View Post
Hmm. I never took the battery cables off. Do you think that is a big step I should do? How long should they stay off?
I don't know if it is a big step or not, but it can't hurt to give it a try especially since it will take a few minutes to pull things apart and clean them. Disconnect +/-
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Unread 01-18-2012, 07:24 PM   #7
ROTTEN
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The tb and sensors are clean. I did the reset
When I restarted it it went to about 1700

Drove around for a bit and came back and restarted. Now the rpms jump to 2400 but go down quick because it's warm

Arg. I might put the 2.5 tb back on it
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Unread 01-18-2012, 08:09 PM   #8
BackRoadJPin
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Sorry Rotten I don't have any other ideas for you, maybe someone else can speak up.
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Unread 01-18-2012, 08:33 PM   #9
dmblair
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I put the 4.0 on mine for awhile and did exactly everything you did. Same thing happened. Idled high for awhile when first starting it after it was warmed up and then it would go back down. That drove me bat$hit crazy cuz I could never figure it out. Threw the 2.5 body back on and it works fine. Wonder if it has something to do with the diameter of the intake not matching the throttle body. I'm assuming you didn't mill the intake for for the larger throttle body right? That was the only thing I could think of that might have an effect on the idle?!?!
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Unread 01-18-2012, 10:03 PM   #10
ROTTEN
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I didn't grind the intake.
I'm putting the 2.5 back on. Then I'll deal with the stumbling. Spring I'll fool with the 4.0 tb

Just too damn cold out!
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Unread 01-18-2012, 10:44 PM   #11
jode
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Crazy, Cuz that is exactly what my 2.5 needs. Right now I have to keep the throttle on in the mornings to keep it running, then, once it warms up I can let off the throttle and it will ease on down to about 1,000 rpm. Maybe I should do a 4.0 throttle body and it sounds like all that will be automatic
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Unread 01-18-2012, 11:03 PM   #12
ROTTEN
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It really sOunds like we both need new idle air control motors
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Unread 01-19-2012, 12:29 AM   #13
jode
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Mine's brand new (my IAC that is)

Is there some sort of temperature sender that interacts with the IAC that may be bad on both of ours?
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Unread 01-19-2012, 12:49 AM   #14
BackRoadJPin
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have you tried using the 4.0 IAC? Interchange them see what happens. I did this 4-5 years ago, and I know I sorted it out with the parts and sensors from the two throttle bodies. It turned out great and gave me a little more pep. However moving to the Seattle area at sea level made just a little more difference.
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Unread 01-19-2012, 10:46 AM   #15
Que89YJ
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2 things. A battery reset to force a relearn and a can or carb cleaner to check for vacuum leaks.
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