Topic: Problem with 4.0 TB conversion

[mjmudd]

Ok, just did the throttle body swap on my son's jeep and having a slight issue.  The jeep won't return to idle...yes we swapped out the AIS housing and everything so nothing but the bare 4.0 TB was used.  It seems that the problem is the throttle returning to bottom position.  We did add a spacer and bracket spacers but the cable does not seem to be in a bind.  The TB was used but appeared to be in fine working condition.  If I push it down it slows to about 1k but otherwise once you start driving it stays at about 1.5-2,000 rpms.  Again, we did swap everything out.  Is there anything that should have been lubricated to help the throttle bottom back out to idle?

Help???

[Jeffy]

Make sure the TB sits flush at the bottom.  It sounds like you have a vacuum leak at the base of the TB.  Some people have mentioned there being a tab on the bottom but I've never run into one of those.

[mjmudd]

I checked it and it was a smooth surface.  I can push the throttle back to the "all the way down position" by hand and it goes back to a reasonable idle.  But using the gas pedal, it just doesn't seem to go all the way back down by itself...like it's sticking.

Thanks!

[sharpxmen]

unhook the cable and see if it goes back down on it's own, if it doesn't go back to idle without you pushing back then it's most likely the shaft bearings or the return spring (sometimes the end comes out  or it breaks of the throttle body). if it does go back to idle then you need to see why the cable binds (maybe it's bad).

[mjmudd]

The spring is strong...it almost returns it all the way back down, just not quite enough to return it to a normal idle position.  It just seems that something is binding just slightly, either the throttle cable or the shaft on the butterfly valve.  Any advice on where and how to lubricate it to rule that out?

Thanks again!!!

[k]

I know the one I pulled was from a salvage yard and was rather dirty (hood was up on the "donor" and the air tubes already had been removed.  I ended up using throttle body cleaner on mine while it was still torn down.  Mine also did not seem to want to close all the way before that.  Also look on the bottom of the TB.  There is a small allen screw that I used to adjust the position of the butterfly in idle.  On that, a 1/4 turn goes a long way.

[sharpxmen]

The spring is strong...it almost returns it all the way back down, just not quite enough to return it to a normal idle position.  It just seems that something is binding just slightly, either the throttle cable or the shaft on the butterfly valve.  Any advice on where and how to lubricate it to rule that out?

Thanks again!!!

you can take the butterfly out, i make 64mm throttle bodies - a lot of them have the bearings seized when i take them apart and i need to work them out with brake cleaner and lubricate them - you can also spray brake cleaner in there and work it out lots and then put some oil in there (better with a lubricant spray so it can get in there good. the seized bearings won't keep the butterfly from coming back though, it could have a ridge formed in the t/b and that might keep it from coming back, if you take it apart and clean it well you would feel that with your fingers.

[mjmudd]

I was thinking about that...taking apart the butterfly and removing the shaft and spring.  Are the shaft and spring and placement of the butterfly screws the same on the 2.5 as on the 4.0?  I was thinking about swaping them out to see if that solves my problem...the used 4.0TB was very clean but I didn't remove the shaft to check it for gunk or wear. 

Thanks and I will post progress,

[sharpxmen]

the shaft is the same length but the 4.0 butterfly won't fit in the 2.5 (the cut in the shaft is shorter in the 2.5).

[mjmudd]

Ok, problem solved, we are all good here.  We took the TB back off and lubed everything up, and lowered the idle screw by 1/4 turn and it runs perfectly.

Thanks to all for the help!!!

Mike

[Bounty Hunter]

Glad you got it fixed.

You can also loosen the 2 bolts holding the throttle plate to the shaft and move the throttle plate around a little so it fits the bore better.  Once it's closed you can tighten the bolts and it should open an close more smoothly.

There should be no need to mess with the throttle stop in the base of the TB.

[k]

There should be no need to mess with the throttle stop in the base of the TB.

Agreed.  There should not be a need, but after cleaning and lubing, excesive daylight could be seen through mine.  It did come from a junkyard though and who knows what happened to it before I got it.

[dwtaylorpdx]

Its pretty common that people fuss with the throttle stop thinking its a idle adjustment.

I can't remember the spec, But your supposed to only have a couple thousandths clearance between the throttle plate and the bore of the throttle body. The stop is to prevent the butterfly from gouging the throttle body wall or bending, all idle air should go through the IAC valve.

I found it in a factory service manual it was not in my Chiltons...

Dave