High idle. Just swapped my 2.5 TB for a 4.0 TB - Page 2 - JeepForum.com
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Unread 01-19-2012, 07:11 PM   #16
ROTTEN
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Sprayed all around with carb cleaner and no difference
Installed a new Tps no difference
Reset the computer no difference

BUT when I turn the wheels while idling the rpms quick jump up 600 and back down
What is that?

Tomorrow im putting the 2.5 tb back on

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Unread 01-19-2012, 09:35 PM   #17
GrantYJ
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The jump in idle comes from the computer. It's the same mechanism that makes your idle jump when you turn the air conditioning on.

As for your high idle, I agree with the previous poster that it probably is a result of you not opening up the hole in the intake manifold. I don't see the point in putting on a 4.0 TB if you don't open up the intake. You won't flow any more air (which is the whole point of the swap). More airflow = more HP.
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Unread 01-19-2012, 10:13 PM   #18
ROTTEN
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Fair enough!

Off she goes tomorrow
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Unread 01-19-2012, 10:26 PM   #19
BackRoadJPin
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Quote:
Originally Posted by GrantYJ View Post
The jump in idle comes from the computer. It's the same mechanism that makes your idle jump when you turn the air conditioning on.

As for your high idle, I agree with the previous poster that it probably is a result of you not opening up the hole in the intake manifold. I don't see the point in putting on a 4.0 TB if you don't open up the intake. You won't flow any more air (which is the whole point of the swap). More airflow = more HP.
I did nothing to my manifold, that is not the problem.
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Unread 01-19-2012, 10:55 PM   #20
BackRoadJPin
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Give this write a read and see if it is of any help.

What sensors do I keep from the 2.5. Which ones do I transfer over from the 4.0

you can transfer the TPS from the 2.5L but seems that they are the same between the 2, to be safe since you know yours is working I would do it anyway.

for the IAC (also known as AIS) you _need_ to use from the 2.5L both the plunger with the motor (sometimes referred to as the solenoid) and the housing that is bolted with 4 tamper proof bolts to the t/b - you should just take those 4 bolts out and transfer the whole thing over, but you'll need the proper torx bit with a hole in the center - they have a ton of thread lock on and are hard to take off, so make sure you don't strip the torx teeth off of it or you'll need to come up with some creative way to take them off afterwards.

if you have the MAP sensor on the t/b (TJ) then you can keep the 4.0L one if it's on there (it's the same as the 2.5L), but again this is if you know for sure it's good.


There are measurable gains to be had.

make sure you changed over the AIS/IAC housing if I remember now that was the problem with my high idle. I just remember I had to play around with the swapped items reset the computer drove it around for a little bit and it worked great.
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Unread 01-20-2012, 09:26 AM   #21
ROTTEN
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Ok we can let this subject sleep the rest of the winter. 2.5 is back on and it's running fine

Few thoughts
I did not change the iac housing. I didn't understand until I took the tb off what the housing was
Also I did not grind the intake

So one of those two things is the culprit


One big change is loss of power. The 4.0 tb Definantly makes a difference.
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Unread 01-20-2012, 09:57 AM   #22
SnowYJ
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So power increase?
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Unread 01-20-2012, 10:06 AM   #23
ROTTEN
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The power increase is noticeable

I really suggest it. 75 in 5th with new 32s. Before I could barely do 65
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