Topic: 4.0L TB SWAP AIS housing question

[bukdwn]

OK. let me see if i can ex plane this correctly!   So i removed the old 2.5L Throttle body and removed both the AIS and the TPS. Both are new.  I fully cleaned up the junk yard fined 4.0L TB.   When i removed the AIS motor, i only removed the motor not the housing that it bolts to. The housing has (4) small security type star bolts and i did not remove that from the 4.0L. From looking at both housings, i could not really tell any difference between the two.   When i went to install the new 4.0L  onto the manifold ,the AIS motor housing has a small de-tent (Sorry for the spelling) witch must be for alignment reasons. So i  got the dremal  out and removed it . The throttle body fit just fine after that!   I re-installed everything and started it up. The normal high idle when replacing the AIS motor but would not come down. Turned of the engine and thought it must be trying to relearn it self.  Turned on and off the engine a couple of times and the idle came down to normal.  The jeep runs great, good mid range. and pulls hills much easier.  The problem is when i start the engine when it is cold, the RPM's stay up around 2000 for about 6 seconds and then it will come down to normal idle.  Do you think this will be fine or should i swap out the AIS motor housings?   

[dwtaylorpdx]

The housing needs to be moved too, if you notice it has 2.5 on it... or something similar.

Use a standard torx driver to remove, just use a small punch and tap sideways in the little pins in the hole and they snap out.

Dave

[chrisfranklin]

Worthwhile if you grind out the intake manifold to match the diameter of the "new" TB.   Forget what the diameter is pre-grind on the 4banger -- its like 52mm or something. 

[knotts89]

They make tamper proof torx bits for those also but the punch should work

[sharpxmen]

They make tamper proof torx bits for those also but the punch should work

yeah, it's like $10 for the set and you get about 20 or so tamper proof bits.

[bukdwn]

From looking at both housings, i could not really tell any difference between the two.  Could you explane what makes the difference between the two? Has anybody tried this before and found that the 4.0L AIS housing works better besides the high idle start?  Buy the way, for the people that are on the fence about this mod. You will not regret installing the 4.0L TB on your 2.5 liter.   There is a hill leaving my town about 1 mile up hill and about 15-20% grade may be more in some areas . I use to be able to get to the top in 4th gear but 38 MPH tops. Now 45 MPH in 4th gear.   A lot easier to cruz down the freeway also.  Thanks guy's for the info!

[sharpxmen]

From looking at both housings, i could not really tell any difference between the two.  Could you explane what makes the difference between the two? Has anybody tried this before and found that the 4.0L AIS housing works better besides the high idle start?  Buy the way, for the people that are on the fence about this mod. You will not regret installing the 4.0L TB on your 2.5 liter.   There is a hill leaving my town about 1 mile up hill and about 15-20% grade may be more in some areas . I use to be able to get to the top in 4th gear but 38 MPH tops. Now 45 MPH in 4th gear.   A lot easier to cruz down the freeway also.  Thanks guy's for the info!

they are different - yes people have tried this before and it doesn't work. they are different size as they are for different engine displacements, the matter is related to air at idle and how much air this IAC (idle air control) valve is letting in, has nothing to do with your speed in 4th gear or anything other than maybe your throttle being opened 1/3 or less. you'll be lacking engine brake and also your revs will come down slower not to mention mpg will also be affected (not by much but it will). other than that they look the same.

[Jeffy]

IIRC, the plunger is larger on the 4.0L.  I've heard some people keeping the 4.0L plunger but I've never seen it done in person.

[Bounty Hunter]

From looking at both housings, i could not really tell any difference between the two. 

Look inside, the difference is the size of the hole in the housing and the size of the tip on the IAC plunger that allows air through to determine idle speed.  Use the 2.5L IAC housing and plunger.

[dwtaylorpdx]

The 2.5 needs about 1/2 the volume of air at idle as the 4.0.

It also affects the off idle transition, the valve seems to act like its
helping balance the transition form no throttle to just opening.

I fiddled around swapping housings trying to figure out if I could
make a idle up solenoid for keeping the alternator up..

Dave

[bukdwn]

you'll be lacking engine brake and also your revs will come down slower not to mention mpg will also be affected (not by much but it will).

 OK, so i did the swap. Changed out the housing, installing the 2.5 into the 4.0L . Also ground  out the intake manifold to match the diameter of the "new" TB. This is what i think. Knowing that the modifications might take a few starts and miles to re-learn it's self. I think it had a little more pull with the 4.0 housing on it. Call me crazy, but i think it had a little more spunk!   I know i need a new air intake to get more air. i still have the stock air box with the mods found on this site.  I'm going to drive over into the bay area tomorrow, so i will wait till then to make my decision if I'm going to re-install the 4.0L housing back on.  As far as what SHARPXMAN said about the lack of engine braking and the engine RPM's  coming down slower! I did not find that to be the case. The only thing was the cold start,  high (2000 rpm) idle for a short 6 to 10 seconds then it would go down to normal idle. I also noticed when at idle, it seems a little higher than  normal, I could not tell buy the RPM gauge if it was higher.  What do you guy's think?

[sharpxmen]

This is what i think. Knowing that the modifications might take a few starts and miles to re-learn it's self. I think it had a little more pull with the 4.0 housing on it. Call me crazy, but i think it had a little more spunk!

since you have a 4.0 and not a bored out (so it's tapered on the bottom, if you'd like i can explain more) theoretically it's possible but nothing that you'd be able to notice on your own. the only thing that would tell you for sure would be a flowmeter, i doubt the result would be of any relevance.

if you say it comes down in revs the same as with the 2.5 housing then you might have something else going on there, maybe your butterfly is not coming down completely or gets stuck or your throttle cable is not moving freely. If you feel it is running better with the 4.0 housing throw it back on there, will not harm your engine or anything like that.

[dwtaylorpdx]

The difference on mine was night and day,,, but,,, I have a balance blueprinted, built engine.
I ended up running the 2.5 TB until the 4.0 TB arrived when I installed the 4.0 tb it really woke
up the enigne.. I also have tri-Y headers, a metal
matrix cat and a spintech muffler so the difference in the top end especially is huge.

Dave

[Nicks92jeeper]

I had the same problem with high idle. I swapped and swapped and then finally swapped out the housing for the sensor as well and it went to normal. I think there might be like a quarter inch difference between the housings but it is enough to really make it sound bad. Just don't break the gasket for the housing. I found my 4.0 at the salvage yard for 15.00, installed it and was happy and leter pulled the intake manifold when doing the head gasket and opened it up as well and was more happy. Verry peppy little engine!

[bukdwn]

Nicks92jeeper,   What housing did you end up with, 2.5 or the 4.0?   This morning i started it up, normal 1800rpm cold start. Came right down to normal idle in about 19 seconds. So i brought up the idle and when coming down from the RPM's it would take a little bit ( about 3 seconds) before it would come down to normal idle.  I removed the + and the - from the battery and let them sit for awhile and re-connected them. Started the jeep and the same thing,   It takes about 2 seconds to come all the way down to normal idle.  I believe the butter fly is not hanging up. Cleaned the TB completely before the install. Also cleaned the motor housing.  I thought maybe a air leak? Sprayed Carb cleaner around the TB and motor housing, Nothing changed!  Yes, i could just change things around but was hoping someone had the same problem, and had a fix.  Trial and error is best but wanted to see what i can find out first!  Thanks for all the info!