great acceleration, really bad braking

[wolfpackjeeper]

Allright, my roomate just bored his throttle body out to a little under 62mm. His idle is crazy high (around 1700) and he can't stop without the use of the e-brake. We tried turning the set screw down as far as it would go, with no gain. We already know he needs a new butterfly valve. Is it possible to rested the tps or buy an adjustable one? what else should we be looking into?

1997 Jeep Cherokee
4.0, AW4. 231, 30'' tires.
great acceleration, really bad braking

 

[Kyjeepdude]

Your lack of braking power is more than likely, lack of vacume to the brake booster. Make sure that you got that hooked back up properly.
I did a little work under the hood once, and forgot to hook that hose back up, and had the same problem. It stinks.
Hope that helps.

 

[natep1]

Did he bore it all the way through?
If he did, is he reusing the original butterfly (I assume by the post but am checking anyway)?
It sounds like the butterfly is too small and that is making it think it is under throttle.
Only cure for that is a proper sized butterfly.
HTH
Nathan

 

[wolfpackjeeper]

its not a vacume line, the only thing he unhooked were the throttle cables. He didnt make a new butterfly valve, im feeling a new one of those. But I also talked with one of the shops I deliver to and he was speaking of needing a way to adjust the tps sensor so it would read the throttle in the right position, he also mentioned needing to reset the IAC. This is a pretty good shop(i.e. the only one that will ever work on my jeep besides me) so im inclined to believe a lot of what he says. He just wasnt cast iron sure without seeing the jeep. Ive never done this mod on my cherokee cause im still not sure its worth it, if we get my buddie's straighted out it might happen eventually.

 

[53guy]

He didnt make a new butterfly valve, im feeling a new one of those. But I also talked with one of the shops I deliver to and he was speaking of needing a way to adjust the tps sensor so it would read the throttle in the right position...

if he didn't get another butterfly, then the one he has is too small, making the TPS go farther down than idle, and the computer is compensating for that. Getting a bigger butterfly will make the TPS sit where it's supposed to, thus making the engine run properly. If he didn't have a bigger butterfly when he put the TB back on and reset his computer, the computer is trying to compensate through out the powerband, so it'll probably make the jeep act funny while driving it around as well. Getting a bigger butterfly should solve his problems, but remember, he'll have to reset his computer as well when he does so that it can "relearn" the new settings.

As far as the braking goes, seeing how the engine is compensating for the TPS, its creating much more power at idle than it should, making it hard to stop.

Is this a good mod to the motor? Yes it is; its the biggest bang for the buck as far as bolt on parts go. Combine the TB with intake and exhaust, you'll feel some more power. All good mods that should be done. :laugh3:

 

[53guy]

by the way, there are companys that make larget butterflys for just such a purpose. i dont remember off the top of my head who makes them, but i know there are some out there that sell parts for bored out tb's. good luck!

 

[JeepFreak21]

First get a new butterfly... otherwise you might as well just prop the friggin' thing open and try to stop.
Billy

 

[wolfpackjeeper]

yea, ive heard great things about it, but ive heard that it can decrease miliage significantly, this is still my daily driver and the 33's i put on mine are already killing milage enough that I have been hesistant to mess wih the throttle body. Sounds like we justneed to get back into the shop and machine him out a new plate, I just wanted to make sure that there werent any other changes we needed to make to it.